If you are still looking for the perfect valentines gift for your special someone look no further. This project is one of the Popular Mechanics 10 DIY Gifts for your Sweetheart this Valentine’s Day. It uses a PIC microcontroller and some RF receiver and transmitters from Spark Fun to detect when the portable unit is close to the base unit.

"This project uses an RF receiver module to trigger a pulsing LED Heart when the transmitter comes within range. I made this for my fiance for Valentine’s Day this year.
In my circuit the data pin on the transmitter is being driven by an output on the PIC. I intend to work more on the PIC program to provide an actual data protocol, but in order to actually get this done this weekend, the transmitter PIC currently just sends a high signal for 500ms, then goes low for 500ms, and repeats as long as it’s switched on. There is an LED attached to the output pin to give a visual feedback of the pulse so you know the circuit is working.
The receiver is equally simple at present. The data pin goes to an input on the PIC. The PIC waits for a high signal, then pulses the LED as long as the signal is high. When the input signal is low, the PIC waits for 500ms, then polls the input again."

Thanks to Tyghe for sending this in.