ElectronicsWeekly posted an article about a company named EnOcean (a Siemens spin-off) which created a light switch wich can transmit RF signals by using the power generated from pushing the actual switch:
Read the entire article
EnOcean.com
Its generators are piezoelectric, providing the 50µW required to transmit the switch's unique code, one of four billion available.
With 7N of force pushing a 3.5mm travel button, the devices transmit 10mW in three randomly-spaced 500µs bursts at 868.3MHz.
Read the entire article
EnOcean.com