Use these radio frequency modules to easily communicate wirelessly in your projects.

There are so many potential uses for these RF transmitter and receiver modules it's mind-boggling. They basically work like wireless wire -- you pull the transmitter data line high and the receiver data line goes high. The units are very small, easy to interface, and above all cheap! Only $13.95 for the set.

With these modules, you could easily communicate with a robot, let your microcontroller read temperature sensors scattered around the house, or monitor the status of the garage door to ensure it's closed each night. Basically, any time you want to transmit data 500 feet (line of sight) or less, at 2400bps or less, this would be useful. You'll obviously want to include some kind of error detection and/or correction in your protocol and if you're going to use more than one at a time, you'll need to encode some kind of addressing scheme, but that's all pretty simple to do with any modern microcontroller.

At $14 for the set, these modules are definitely cheap enough to embed in anything that you feel like, unlike many radio communication modules which cost just enough that deploying several just to read sensors for a frivolous project is not reasonable. The top-level site also has lots of other interesting prototype supplies like breakout boards for SD and CF flash memory cards. It's definitely a site to bookmark for your electronic projects, especially if you use PICs, AVRs, or other microcontrollers.

UPDATE: SparkFun discontinued the ones I wrote about initially, so I updated the above link to a similar item. There are also 4800bps modules and a couple different frequencies available on their wireless modules page.