This project describes how to wire up a simple telephone intercom, whereby you will be able to converse with the person on the other end. It does not describe how to wire them up so that the ringers work, as this is quite a bit more complicated. Instead, you can rig up a circuit using a pair of buzzers or LED lights and a couple of switches (only if your telephone cable has 4 wires) in order to get the other phone to signal an incoming call.

It also should be pointed out that these phones will be completely separate from the other phones in your house- do not try to wire them into your current telephone wiring system!

Cup phone

Materials and Tools

2x old telephones

a power supply

telephone cable


soldering iron and solder

electrical tape

Step 1

Figure out where you'd like the telephones to be, and how you will route the telephone wire between them. If the children would like the phones in their bedrooms you will probably want to be able to hide the wire discreetly somehow. The phones will also have to be connected to a power supply, so the wire must pass a wall power socket somewhere along the line (unless you are planning on using a battery).

The other option is to use cordless phones, which in effect will create walkie talkies, however consider the ability of children to misplace things and lose the handset.

Step 2

Find a suitable power supply. You will need one that is around 9- 12V and no more than 30mA current (you may need to wire in a resistor, depending on the output of your power supply). I used a power adapter I had kept from some old long-discarded device which works perfectly- I just snipped off the plug at the end, stripped the wire back and wired it straight in. Otherwise you may have to purchase one from your local electronics store.

Step 3

Wire up the circuit as per the diagram. Use only the red and green wires from the phones. Test the phones prior to soldering and wrapping electrical tape around the joints.

telephone intercom

Step 4

You have finished!