I will have a look for a wireless sender, but CPC and Maplin both do cheap modules.
Or you could use a wireless door bell and modify it slightly with a different switch soldered to the original contacts. They cost about £15.00, just stick the whole thing in a waterproof plastic box from RS comonents or something.
Or you could use a wireless door bell and modify it slightly with a different switch soldered to the original contacts. They cost about £15.00, just stick the whole thing in a waterproof plastic box from RS comonents or something.