I'm having a bit of an issue (maybe in using the correct search terms) finding a key fob-like thing that can be received on the Arduino by a single receiver (ie. you can't get another key fob to work with the receiver without setting it up first).
I have thought about building another device with a transmitter however I'd prefer to try to have a look for a simpler device that'll do it for me rather than going to that effort, also, pre-made things are more compact. The range should be >= 100m or so.
The reason is the system I'm building should not be accidentally triggered on the off chance someone nearby has the same type of key fob or a compatible one.
I researched this somewhat, comparing a common garage-door opener device. Requirement for a thousand feet puts the project into a more expensive realm than the garage door opener. You begin looking at telemetry solutions. ATMEL has recently purchased at least a couple companies, looking to develop more RF products. It may be worth waiting for a new product from ATMEL.
I'm interested in giving the garage door opener IC an SPI interface. Look at the MCP20S08 and figure that the IC provides an interface, not port expansion. Looking at the chip functionality backwards sort of opens the door to a project you can prototype before selecting a microprocessor.
There's a decoder which can "learn" the codes of different key fobs in their range and I assume each fob has a unique code.
EDIT: From the receiver data sheet: "Each RF Solutions transmitter contains a secure serial identity. When a switch is pressed, the transmitter emits a unique secure RF signal. The Receiver can learn this signal and allocate it to any of its output(s)."