Is it possible to wire a photocell in sutch a way, when light is on it, nothing will happen, but when the light is broken, it sets an alarm off or something?
Is it possible to wire a photocell in sutch a way, when light is on it, nothing will happen, but when the light is broken, it sets an alarm off or something?
Yep. It is often called a "beam-break trigger", "dark detector", "dark alarm", or various other names along those lines. You can google those terms or search this site; it's been discussed a few times.