No I only know that have the same groundThis is sounding like homework, and should be in that forum.
Are you allowed to make measurements on Device1 before you design Device2?
Your question is unclear. Do you want to use a reed switch removed from Device1, for use in Device2 that you are building? Or do you want the reed switch to simultaneously perform its original function in Device1 while also switching something in your Device2?
One feature of a switch is that the voltage across it changes dramatically when the switch changes state. A clue to consider.
by Aaron Carman
by Jake Hertz
by Aaron Carman