Wireless PC Lock is just £9.99 inc Free delivery from blahDVD.co.uk
EDIT: Price gone up to £17.99
Cool gadget for a budget price. May be even cheaper than ebay !
Description: Central Locking for your PC. Simply plug the USB device into your USB port, and whenever you move more than about two metres away from your computer (whilst carrying your 'remote' receiver), your computer automatically locks itself! When you get back to within two metres of your computer it unlocks again. Once the computer enters the "Lock Mode" a password is required to use the computer again.
Specifications: Operation frequency: 434MHz | Transmitter power supply: DC 3V (included) | Battery usage: approximately 2000 hours | Receiver power supply: DC 5V provided by the computer through the USB port | Software driver: supports Windows 98SE/ ME/ 2000/ XP
Special Features: USB central locking key | Remote control locking unit | Effective range about 2 metres | Auto-lock when you're away from your computer | Transmitter uses a DC3V battery (included) | USB receiver size: 70 x 20 x 10 mm | Remote control transmitter size: 10 x 30 mm diameter