The StrikeFinder V2, built by StrikeFinder in St Antonio, Texas is a small camera mounted device that plugs in to the shutter release port on the camera, has an on/off switch and a little red LED and that’s it.
Very simple in its outward design; it doesn’t need fiddling with or connecting to an external source for control input. Internally it is very similar to the original StrikeFinder, an Infra Red detection circuit coupled to an ATMega368 (that’s the reason mine was open, I find the ATMega368 is prone to noise, especially lightning generated, so with many years of experience around guitars I also ground shield the triggers). The biggest difference between it and the original is that it’s got an automatically setting sensitivity circuit, and also has focus locking as well.
The last I bought were 110€ each, direct from manufacturer : http://www.strikefinder.photo.