So how do spies communicate? Secret codes? Walkie talkies? Mobile phones? Have a go at making a telephone but make sure no-one else is listening in…
DIY telephones
Ask an adult to help you.
You will need:
- a long piece of string or nylon twine.
- two plastic drinking cups
What to do:
- Pierce the bottom of the cups with a needle (be careful – you may need an adult to do this bit)
- Thread the string through the holes in the cans. Secure it by either tying a knot on it, or taping a loop of it to the inside of the bottom of the cup.
- To work, the string has to be pulled tightly between the two cups. You and your ally can take turns to listen and speak to each other.
- To transmit, hold the cup up to your mouth and speak into it. (Or you could tap out a code instead for extra security!) To receive, hold the cup up to your ear.
- You may feel that you can now have a private conversation, but is your transmission secure? Enemy agents may be able to tap into the signal and listen to every word. They could do this by simply tying a third cup to the middle of the long piece of string, and if so, they’d be able to monitor your communications. As long as they stay silent, keep hidden (and don’t jiggle the line due to giggling), you may never know they are there. So be careful!!
How does it work?
Sound waves are vibrations that can be carried through the air and solid objects. When you speak into the cup, you cause air molecules to vibrate and the vibration is transferred to the cup and then the string. If the string is held taut, the vibrations can travel down the string to the second cup, where the vibrations set the cup vibrating and the cup causes the air to move! By tying a third cup to the string the vibrations in the string are divided between all three cups.
In real life phones are tapped all the time without people knowing. This is particularly true for mobile phones since the signal from your mobile phone can be picked up by anyone with the right equipment. Mobile phones transmit signals to the local receiving station, where they are retransmitted to a satellite or another base station. A spy can scan all the frequencies that the receiving station can pick up and so listen in to any phone call made in that area. Oooooh how sneaky!
