Karen Nakamura: January 2011 Archives

A simple circuit that flashes an LED when the phone rings -- with an alternate version that closes a relay when the phone rings.

http://www.circuitstoday.com/ringing-phone-light-flasher

and this kit gives an excellent schematic of how to do this: http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k8086.pdf