wvmarle:
Sure... have the Arduino interface with an RFID reader, and when it finds the correct tag switch on a relay. Very simple.To not drain your bike's power supply you at least have to go barebones (i.e. get rid of the Arduino board overhead), use power saving techniques such as sleep (just wake up every 0.5 seconds to check the reader), and a low-power RFID reader to match. Maybe even add a physical switch to switch off the system when not in used for a long time (e.g. when parked at home for the night or even a few days).
I would be totally fine keeping the physical switch to conserve power. What about Bluetooth? Possible to energize relay if within range of Bluetooth phone?