I have received several emails asking how to connect up some lights so that when the phone rings, they flash. This is very useful in a situation were there is lots of noise and it is impossable to hear the phone, such as a workshop. Here is such a device.
# You may need to use a lower voltage zener for D1 and D2.
# You can use a regular relay instead of a solid state relay, but the arcing accross the contacts may destroy it pretty quickly.
# Be very sure that you have not accidentally connected 120V