Wiring up multiple doorbells to a single bellpush button

Sometimes it's useful, or necessary, to have more than one doorbell ringer placed around a building, or multiple buildings, so that it's possible to hear the doorbell ring no matter where you are.  This is not completely straight-forward to do with most wired doorbells that you buy from the hardware store, but is do-able with a bit of ingenuity.

The alternative, of using wireless doorbells with multiple receivers is possible, but doesn't always work in practice.  You mightn't be able to pair multiple receivers to one bell push button, the range of the signal mayn't spread as far as you need, or penetrate through the walls, or suffer conflicts with other wireless systems.  And batteries will go flat, perhaps unnoticed for many days, though you can get battery-less bellpush transmitters with mains powered receivers.  Those were the problems that we faced, while trialling various unreliable wireless systems over time, so we went with a wired solution.

I've stayed completely away from WiFi and internet-dependent gadgets.  It's a pain dealing with accounts, and relying on outside services for things like a doorbell is ridiculous.  Doorbells are something that should work forever once wired up, without any further fiddling around.

It used to be easy to buy good doorbells from the local stores, but in recent years the traditional ones have gone away.  There's electronic ones which sound like singing mosquitoes (damn awful), or simply aren't loud enough, and wireless ones that have shortcomings that didn't work reliably in my house, as I'd just mentioned.  I've come to the conclusion that wireless doorbell transmitters and receivers really need to be within arm's length of each other to be reliable, about the only advantage being you don't have to drill through a wall to wire them together.  Hence my DIY project to come up with something much better.

DC doorbells

One problem with wired doorbells is similar to wireless ones, distance—as the length of your wiring increases, you lose voltage along it, and mayn't be able to make a bell ring at the end of a very long wire.  Or, more to this point, mayn't be able to make multiple bells ring.  But you could be in luck, and may be able to simply wire up a system like this, using traditional electro-mechanical doorbells:

A single power source (usually a battery) goes through the front doorbell button, and goes to each doorbell ringer in parallel.  Essentially, you're giving power to the solenoids that strike the chimes or ring the bells.  However, you will need to modify each doorbell ringer, so you can wire-up directly to their solenoids, and remove their batteries.  There's several ways to do this.

1. Link directly to the solenoid in each doorbell, ignoring everything else in the doorbell (as per the above diagram).
2. Short out the remote doorbell's switch terminals with a wire, and link this doorbell to your wiring via its battery terminals
3. Short out the remote doorbells' battery terminals with a wire, and link this doorbell to your wiring via its switch terminals (as per the below diagram).  The advantage of this method is that it gives you two screw terminals to connect your doorbell wiring, and the internal battery-shunt modification is very easy to do.

You need to link all the doorbells with the correct polarity.  If you get it wrong, they won't ring (or ring properly).  Just swap its leads over if that happens, mechanical doorbells shouldn't be damaged by reversed polarity.

But if you're like us, and needed to place bells at the ends of very long wires, the furthest ones didn't work with that arrangement (they didn't ring, at all), and an alternative is needed.  You can try heavier guage wire, but that mightn't be enough to make things work, and rewiring is an awkward and expensive thing to do.  Another option is to use a stronger power supply, but that can overwork the nearest bells, so you'd need to reduce their drive voltages.  You could put some diodes in series with their solenoids, as simple voltage droppers, like this:

But again, that mayn't be enough to deal with very long wiring runs, and it's rather experimental to work out how many diodes you'd need at each ringer to reduce the voltage.  And not practical if you're using AC-powered bells (you'd need a second set of diodes, in parallel, facing the other way, or use series capacitors as voltage droppers).  Yet another option is to reduce the amount of power required to activate each doorbell ringing.  We went for the latter, and wired up a system like this:

A single power source (a small battery) goes through the front doorbell button, and two wires from this (marked A & B) go to each doorbell in parallel.  At each remote doorbell is a small relay that only needs a small amount of current to activate, and it's this relay that's powered by the front doorbell button (the A & B wires go to its coil, polarity is usually unimportant, though I've found one relay that was).  The contacts of these relays go to where the remote doorbell would have had its own press-button connected.  Each doorbell has its own batteries, and operates just like a stand-alone doorbell normally would.

It works rather well, and allows us to use any doorbell without having to modify them.  We just use our relay-interface switch contacts instead of their usual push-buttons.  All the batteries last many years, since they're normally not supplying any power to anything.  If the relays are small units, you may be able to power them from a single 9 volt transistor radio battery at the main doorbell button.  That's what we've done.

This technique makes it easy to run almost as many doorbells as you'd like around a property (inside, outside, several rooms).  And you can unplug individual doorbells when you don't want to be disturbed, without affecting the others.

The one difficulty is if you use an illuminated push button.  Most of them work with the globe across the switch, so there's a continual drain of current, making battery power unsuitable at the pushbutton.  You need a small power supply transformer that's designed to always be connected to the mains.  Many power supplies are not, so look for ones specially rated for always-on/24-hour use.  You can buy supplies made for doorbells, modems, and alarm systems that are rated like that.

There's a second problem with illuminated push-buttons, in that the globe may pass enough current to activate all the relays, permanently.  They tend to rely on the usual doorbell solenoids needing a hefty amount of current to strike, and the globe will not provide this, but it may supply enough current to activate small relays.  A LED-illuminated doorbell button needs far less current to light, and may be a solution.  Otherwise, you're faced with modifying the push-button enclosure, to power the light separately from the switch mechanism, or completely removing the light from the switch.  I found I couldn't use an illuminated push button, at all, with my system.

This system served us reasonably well for many years, and being battery powered meant that the doorbells worked even when the power was out.  Though there were a few things I didn't like about them:  I could only get my hands on some poor quality electro-mechanical doorbells that didn't ring that loudly, most shops had stopped stocking the old fashioned ding-dong doorbells.  Changing several batteries every year or two was annoying, and not environmentally friendly.  And a surprising number of people seem to be incapable of ringing a doorbell properly, I ended up putting a sign saying “ring the doorbell like you're actually trying to get my attention.”  And, even then, some people just lightly touch the button for a microsecond, as if they didn't want you to answer the door.

AC doorbells

The above section was all about DC powered doorbells with the electro-mechnical solenoid to make a ding-dong sound.  Many years later I looked into using AC doorbells, the kind that ring constantly (like an alarm bell) while you keep your finger on the button, and found I had greater luck with directly powering them from one common source than the ding-dong bells (because the bells I tried it with didn't need as much current to ring).

I'd had an unexpected problem with the ding-dong bells, in that a surprising number of people don't know how to use a doorbell—they'd hold their finger down on the button, and you just get a dull clink-clunk instead of it ringing loudly.  And even with those who pressed it properly and let go, you only heard one ding-dong, and could easily miss it.

Whatever type of doorbell you have, people are more likely to use it properly if they can hear it ring when they press the button.  So it definitely helps to have one ringer within earshot of the door.  And I think it's more important to be able to hear someone urgently trying to get your attention in an emergency, than worrying about the rare occasion when someone makes a nuisance of themselves ringing your doorbell.

Doing a bit of electronics recycling at home, I had two of the old mechanical telephones sitting around the place that hadn't been used for around a couple of decades since we replaced them with touchtone phones.  So I thought I'd try repurposing them as the doorbells, and have been quite pleased with the results.  And one advantage with using telephones is that they're a self-contained box that doesn't need to be mounted.  Of course you could mount the phone somewhere, or take the bells out and mount them out of sight, or in a box.

If you run about 30 volts AC into them, their bell rings quite decently, and 30 volt transformers are easy enough to get from electronics shops, as well as it being a safe low voltage.  Telephone bells are very low current devices, only needing about 5 mA to ring, so you only need a small transformer.  They work well over long cables (there could be a few kilometers of cable between your phone and the exchange, they had to be able to work over long distances), and you shouldn't need heavy-gauge wiring to connect them.

And as yet another bonus, many houses already have phone wiring throughout them that it isn't being used any more (people use mobile/cell phones, instead, now, and the modern broadband installation has often disconnected them).  On that note, you have to ensure that your house internal phone wiring is completely disconnected from the outside world before you use it for something else.  If you can't, then you must use completely separate cabling for this.  But once it's isolated, you only have to make one connection to it, the interconnection between all the sockets is already wired the way you'd need it to be for this doorbell circuit (ring current applied to the bell wiring rings the bells in the phones).

Stereo loudspeaker wiring is quite okay for wiring these kind of doorbells.  They don't use a lot of current, and even an extremely loud stereo system doesn't go much above 30 volts, so the cable will be quite suitable.

The circuit is very simple.  A low voltage AC supply goes to the bell push, and from there to the phone bell(s).  It's the same arrangement as the first circuit shown for the DC doorbells, at the top of the page.  All the phones are strapped across in parallel, in the same way that house phones are usually wired together.  The main reason this worked better than the DC doorbells, was that the phone's bells didn't need as much current.

For safety's sake, I've put a 500 mA fuse in the primary side, likewise in the secondary side.  The circuit doesn't use anywhere near that amount of current, but in the event of a transformer failure, or someone nailing through the bell wiring, no disasters should happen.  It's a slow-blow fuse, so you won't get nuisance blows when the power is first switched on.  And if a transformer developed a short, it's certainly going to draw enough current to blow that fuse straight away.  I don't think the secondary side needs a slow-blow fuse, the bell coils use a tiny amount of current, less than the transformer does when energised.

If a larger bell, that needed more current, was used, then a higher secondary fuse would be needed.  But don't exceed the current rating of the transformer.  Minor transgressions for the brief moment a doorbell rings would probably be okay, but not larger or longer ones.  For instance, I wouldn't be concerned about momentarily drawing 1.3 amps from a transformer rated for 1 amp.  It's probably going to manage to supply what you need, not going to get the chance to overheat, and may even still be within tolerance of its ratings.

Your transformer may provide specifications for the fuses to be used with it.  If it does, stick to them.  The primary fuse should be as specified, else it's liable to nuisance tripping, or not tripping when needed.  The secondary fuse value should be close to the capability of the transformer's maximum current rating, and your transformer ought to have more capacity than you're actually going to use.  Using slow-blow fuses is advisable with inductive circuitry, like this.  They shouldn't nuisance blow under normal use, but they will blow quickly under high-current fault conditions.

Some transformers won't need a fuse (I've never seen a wall-wart plug-packs with one).  Either they've got one fitted internally (I had one where the specs said so).  Or, it has such low current capability that perhaps its short-circuit current consumption is not that much different than it supplying its full capability, normally.  Considering that until you press the bell-push, no current is being used, and you only press it for a brief moment, it's unlikely any damage to the bell wiring would be catastrophic to the transformer, unless you used a ridiculously over-sized transformer.  If the bell doesn't ring when you press the bell-push, you know there's a fault that needs rectifying.  But a small fuse is cheaper than buying a new transformer, and quicker to change.

My transformer also has an internal thermal fuse, that's also advisable.  Should the transformer seriously overheat (because of some fault, not through normal use), it'll melt its fuse rather than catch fire.  Thermal fuses are designed to blow at temperatures high enough to melt the transformers insulation, which would be well over 100° C (according to one manufacturer).  This is a one way trip, by the time a thermal fuse has blown due to this kind of fault, a transformer is no-longer trustworthy, and considered disposable.  While thermal fuses can nuisance trip, that tends to be an very old age problem, I'd never expect a new transformer to do that (certainly not in any decent quality transformer).

In a low-current application, like this, the transformer should only ever be warm.  While some are less efficient than others, I wouldn't expect any to get too hot that you couldn't keep your fingers on them continously.  Out of the two that I tried, a small one reached 40° C, a larger one reached 34° C.  It spends most of its time doing nothing, and a tiny amount of time barely doing anything (when the bell rings for a few seconds).

My phone bells only used 5 mA (each), so the secondary fuse could be reduced to an even smaller value, such as 125 mA, remembering that the initial current may be a bit higher than you read with a multimeter in series with a bell that's ringing.  Also remembering that the currents add up (two 5 mA bells draw 10 mA together).  But even with a 125 mA supply, you can expect to comfortable drive well over a half a dozen such bells.  Of course if you want to add extra things, like indicator lights, you may need a higher fuse.  Just ensure you stay within the specifications of your transformer, use a bigger one if needed.

The transformers I tested used about 5 watts when idle, and just a fraction more when the bell was ringing.  With my high local electricity charges of 40¢ per kWh, that's about $3.50 a year, less than the cost of batteries, never having to care about them leaking acid, and eliminating having to change them ever again.  I found I had to change my doorbell batteries about every two years (they had poor shelf life, more so than being flattened by actual use, especially since modern battery formulations aren't allowed to use mercury).

I found it did require an old-fashioned phone with a mechanical bell.  While the modern all-electronic phones did ring if someone kept their finger on the button for a long-enough time, a short press of the doorbell button wasn't enough to start them ringing.  And a modern phone with caller-ID display didn't work at all, it was probably fussier about wanting an on/off pattern of ring current.  And, of course, it should work with telephone extension bells that aren't actually in a phone.

Although it's often stated that the ring current for a telephone can be around 50 to 100 volts, almost all the phones that I tried would ring from about 30 volts.  If yours don't, you've got two choices: use a higher voltage, or a different device as your bell.  If you can't buy a transformer with a high-enough output voltage, two separate transformers of the same type with their outputs wired in series will give you double the voltage.  But staying below 50 volts is advisable for safety, and for staying within the less-restrictive regulations of extra low voltages (ELV).  All phone bells should be able to ring with 50 volts, they would be much good if they didn't.

You don't have to modify the phones, just plug them in (you can get sockets to suit).  Phones are designed to ring their bell when a suitable AC voltage is sent to them through their normal wiring.  For modern phones, with the tiny 6-pole jacks that look similar to ethernet, the middle two pins are the standard pins to use (voice, dialling, ringing, all the normal phone functions are done over just two wires connected to those pins).  For the last of the Australian phones with the very large plugs, pin 2 was voice, dialling, and bell, and pin 6 was common.  And for very old Australian phones, pin 2 was voice and dialing, with pin 3 for the bell, and pin 6 is common.  You can simply wire pins 2 and 3 together in the socket so they'll work with any phone, that's the standard way most wall jacks were wired.

While I've said you don't have to modify them, there is one reason why you might want to.  Although the bell only uses a small amount of current, the voice and dialing circuit will put a significant load on the circuit if you pick up the handset.  One I tested would draw around an amp, if I did that.  The phone system is designed to detect the handset being picked up, by the load it imposes on the line, and abort ringing the bell.  This doorbell circuit won't.  There's a very simple solution to this with old mechanical phones, disconnect the voice and dialing circuits.  This can either be done by unhooking pin 2 in the large plug and socket, or undoing the jumper for it inside the phone (the phone will have a schematic inside it, or you can trace the wire back from the plug).  Otherwise ensure the handset is always hung up on the phone body.

Of course, if you don't have old telephones handy to repurpose, you can get stand-alone mechanical bells with 24 volt coils (businesses often use them at their deliveries entrance, and they're used with alarm panels).  Of course you'd use a slightly lower voltage transformer with them, they mightn't survive being powered from 30 volts, they really should be powered from 24 volts (or whatever voltage they specify).  They'll probably require more current than the telephone bells do, one I tried was 24 volts at 1 amp, but you ought to be able to find a ready-made power pack for them.

Be aware that stand-alone bells can be very loud (particularly alarm bells), you might want to place stand-alone bells high up near the ceiling, or in an adjacent hallway, or even inside the ceiling.  With one of these bells, you mighn't need multiple bells around the property, just one loud bell in the middle.  The one I tried was quite loud enough inside the hall closet.  One central doorbell was traditionally all that was needed in a house, but in the modern world of people playing loud music it isn't always enough.

I'd steer away from 120 or 240 volt bells, it's just too risky for wiring things like that yourself.  Though you could run 30 volts around the house, and then wire a 30 volt transformer backwards at the bell location.  But it's far safer to stick with everything well below 50 volts.

If you don't feel confident building power supplies, or your local regulations don't permit it, you can buy ready made power supplies.  You may find it hard to find AC supplies above 24 volts, and have to wire the outputs of two transformers in series (as per the diagram below).  Alarm panels frequently used 16 volt AC plugpacks, and two (or more) of them wired together will do the job.  There's nothing wrong with doing that, it's how multi-tap transformers work (multiple interconnected coils), though I'd only use same types of transformers together.  And as mentioned, phone bells could be run from 90 volts, so there's a lot of leeway for running them from higher than 30 volts.  Around 50 volts should be more than enough.

It's easy to get the wiring the right way around.  Wire it up as per the above diagram, then measure the output.  If you've got it right, it'll be close to double the voltage of the individual transformers.  If you've got it wrong, it'll be close to zero, and you'll need to swap the wires over from one of the transformer secondaries.  And if you haven't got a meter handy, use one of the bells.  The correct wiring will be loud, the wrong wiring won't ring, or will be very quiet.

NB:  Each primary should be protected by a fuse, and for the most predicatable behaviour (so it either works properly, or not at all), I'd use one fuse leading to both primaries.  Of course that's only practical if you were fitting two transformers inside an enclosure, as opposed to using two separate prebuilt unmodifiable plugpacks.  As to where to fuse the secondary side, I'd probably put it in the link between the two secondaries, and that's something you can do with plugpack supplies (link and fuse their outputs inside your own enclosure—some kind of junction box where all your cabling comes together).

Other considerations

Do not disturb

Sometimes you don't want to be disturbed, so it can be useful to able to switch off a doorbell completely.  While you can obviously hang a sign on the front door, you can enforce this with a centrally powered doorbell system by switching off the power.  If you were a shift worker, you could even put the doorbell power supply on a time switch, to automate this.

You could be more nuanced with distributed doorbells by having doorbells that are quiet enough so you'll only hear it when you're in the front room, and use remote doorbells that can be switched off or simply unplugged.

On the other hand, you might be best not muting the doorbell.  For example, if your neighbour spots a fire, you really do want them to be able to get your attention at any time of the day or night.

Visual indicators

If you're hard of hearing, or in a noisy environment, it can be handy to have a visual indicator that the doorbell is ringing.  It's not too hard to rig up some LEDs so they'll light up at the same time.  And if you feed them through a bridge rectifier and a large capacitor, you can make them stay illuminated a bit longer than the bell rings.

Junction boxes, and plugs & sockets

Rather than hardwire everything together, make it so you can unplug things.  That way you can change batteries or fuses without having to work in an awkward spot.

For plugs and sockets use something that's unique, or won't be mistaken for something else.  Don't use a common connection where the wrong thing might be plugged in accidentally.

Though, in my case, for the AC bells I did use the old-fashioned large Australian telephone plug and sockets, using the terminals that would normally be used for a bell in a telephone, with the same kinds of voltages that I'm using.  And such phones are no-longer in use, anyway, the wiring isn't connected to the outside world any more.  This made logical sense, since I was using telephones plugged into this as the doorbells.

For my earlier DC bell trial, I used 2-pin DIN speaker connectors.  The only other thing in my house using that kind of connector was an old Super 8 film projector, and there's no way I'd be accidentally connecting that to the doorbells.

Alternative sounders

You can get AC or DC powered bells.  DC powered bells can generate electrical noise as the bell current is switched on and off by the striker, this may be a nuisance to radio and television reception.  AC powered bells don't do that, the alternating current causes the striker to move back and forth.

If you find bells irritating, or you're insensitive to the high pitch of them, you could try a buzzer.  They're generally lower pitched.

If you want a very quiet buzzer (e.g. to sit one right next to you on the desk), you could put a relay in a small box.  AC into a DC relay coil would buzz, or DC into a DC coil relay through its normally closed contacts (when the relay energises, it open the contacts and disconnects itself, then reconnects itself in a continuing cycle).

Wiring mistakes

Don't try using a multi-tap transformer like this diagram (below) to drive devices with different voltages.  The first drawing appears to be what you want, at first glance (two parallel switched bells).  But if you think more about it, you realise the second drawing is the circuit when the switch isn't being pressed (two bells in series, always being powered on, from a lower voltage).

The right way to do it is something like this (pictured below), either with a double-pole switch (which you won't find with a traditional doorbell pushbutton), or using relay contacts (here) instead of push switches (the bellpush switches on the relays, the relays power the bells, done in the same way that I dealt with the doorbells in the DC doorbell section at the start of this page).  And yes, you can get relays which have AC powered coils, if you don't want to horse around with DC rectifying AC to the relay coils.

Don't put a bellpush switch on the mains side of the transformer, most of them are not designed to be safe in that configuration, even if they say the contacts can switch 240 volts.  They're mounted outside, not waterproof, and the bare wiring and switch contacts can be touched.  Even on a dry day, you could accidentally spray it with a garden hose, or someone pressing the bell-push with wet hands could be zapped.