How to Make Spy Items

Eavesdrop. If you want to know what's going on, hide and listen in. If that's not a practical option, you can listen in from another room by hiding a baby monitor under a piece of furniture. Alternatively, you can modify a pair of walkie talkies. Press the "talk" button on one of the walkie talkies and hold it down with tape. Plant it in an inconspicuous place and listen in from up to a mile away. In many cases, walkie talkies are the better choice because they run on batteries.

Send a secret message. Create a code and write in invisible ink. Using slightly off white paper (such as recycled), write your message in lemon juice by dipping a pen that has the ink cartridge removed into a cup and writing as normal. When held up to a heat source, the lemon juice will turn brown.

Create disappearing ink if you need something more discrete than lemon juice. Place 2 tsp. of rubbing alcohol in a small container. Add 1/10 g of thymolphthalein and stir to dissolve. Add 90 ml of water and stir well. Using an eye dropper, add approximately 20 drops of sodium hydroxide, stopping when the solution turns dark blue. Write carefully on paper as this sort of ink takes longer to dry. To make the message reappears, gently rub the area with a cotton swab that has been soaked in ammonia.

Turn the screen off on your laptop, but leave the computer on and the Web cam running. When you leave the house, the Web cam will record everything that is said and done in your absence.

Dust for fingerprints. You can make a version of fingerprint powder by using a coin to crush graphite from a pencil. Once the graphite is evenly ground, sprinkle it on to the area you think prints might be. Gently twist a large powder makeup brush over the area to reveal the print. Lift the print with a piece of clear tape and attach it to a blank index card.