I had built an Electrocardiogram inside a WRT54G case with my partner Hartley Schroeder for our engineering final project. We're done the class now, but I thought I'd post the link to the project in case anyone was interested in the files or anything:
http://code.google.com/p/projectguardian/
http://www.youtube.com/watch?v=A20e6lwiCK0
The serial into the router was the only part that didn't work, and unfortunately it was fairy essential for the GPS input (with gpsd) and the microcontroller connection (after failing to get SPI working for our SPI Analog-to-Digital converter). It even had txt message notifications for a sudden drop/rise in heart-rate to the patient or their doctor.