Keysender No. 5 (Keycaller)

Key sender
Key sender

No, it is not a telephone. It is however telephone related. It is an aid for switch board operators. This device enabled them to dial a number quicker and freed them to help other callers, while the key sender continued dialling the required number.

They were introduced in the 1930s and used by GPO in the UK, but also in other countries too.

I bought mine at a swap meet in the UK, as you never see these devices here in the Netherlands.
For promotional purposes it was sometimes called a keycaller.

It is basically a large metal box with 10 typewriter style keys. Inside is a mechanism with clockwork gears and a large white indicator wheel with small lines on its outer edge. Through the indicator window at the top this wheel shows whether the keysender is engaged or not.

The advantage explained

Key sender keys
Key sender keys

The advantage of the keysender is twofold.

Firstly, because it is a push lever system, there is no need to wait for the dial to return to its resting position before you can dial the next digit, like you would on a normal rotary dial. This saves on average o.5 seconds per digit.

Secondly the next digit can be dialled before the keysender has finished dialling the previous one. So a sequence of digits can be punched in in a short time, the keysender keeps sending sends out the number dialled with the normal 10 pulses per second, after the operator has finished punching it in. So the operator can perform other tasks, while the keysender is busy processing the number dialled.

How does it work?

Key sender inside
Key sender inside

The mechanism has a large wheel with small movable pins along the edge. When a key is operated, one of the pins is depressed. When the next key is operated another pin is depressed. The space between the 2 corresponds to the number on the latter key. So if the number 4 is pressed, 4 pins are left and the 5th is pressed in.
So, for example, when the number sequence 2, 4, 1, 5 is keyed in, the row of pins will look like this:

The mechanism rotates the wheel with pins, activating the pulse contacts. After each digit the pins are pushed back up. So the wheel serves as a mechanical memory of the digits of the telephone number that is keyed in.


The keysender was used mainly in the British Commonwealth. It is a solution to keep lessen the burdon on switch board operators, as telephone traffic started to increase in the 20th century.
There were other solutions to this problem. In the USA they used rotary dials operating at double speed. So they sent out pulses at a rate of 20 per second. The problem with this method is that you need to adapt your exchanges to be able to receive this higher pulse rate.
The Germans had a kind of pull down dial, similar to a drum dial. Because of the ergonomics of its design, the operator could dials a little faster than with a normal dial.
So a special dial to aid switch board operators was in itself not unique, but one with push buttons certainly was.

Well, at least not until the advent of tone dialling with micro-electronics, that is.