Bluetooth® is the short range radio based data system used for a myriad of locally connected devices. Such devices include hands-free car phone systems, wireless serial cable replacement, printers and many other computer peripherals. Recent work on a telemetry project with Bluetooth® modules being controlled by microcontroller and sendind data to and from mobile phones with a custom built Java app has opened up new possibilities. All of the sensor techiques mentioned elsewhere on this site can now be used via mobile phones over short ranges and with very low power consumption. You could perhaps control a device via your phone or have your phone monitor and alert you in the event of a situation of note occuring - like joining a bite alarm to a mobile phone perhaps...