What kind of "switch" component detects current?

[Streaksy]

I know some absolute basics of electronics and I've been bodging for years but I want to do it right this time.

I mutilated a PC joypad to give my PC a bunch of extra switches for various tasks, and I make scripts that react to the buttons at any time, by reading the PC joypad input buffer. The thing is I want a wireless switch and I usually use a cheap wireless doorbell for this kind of thing, and replace the speaker with a motor which physically joins two terminals together when powered. There's got to be a better way.

I'm thinking of buying a wireless doorbell, unwiring the speaker completely, and using some kind of switch that detects the current that would usually be going in to the chime indication light.

So what I'm asking is: is there a component that reacts to a small current by completing a second circuit? - Or you could call it a switch that is made/closed by power in a second/external circuit. If I have the answer to this my lame, amateur electronic problem solving will really be stepped up.

Thanks.

 

[(*steve*)]

Depending on various other (unknown) requirements, that component might be:

1. A BJT (a "normal" transistor)
2. A MOSFET
3. An optocoupler
4. A relay

Your question (if interpreted literally) is so broad that many other things could also suffice.

If the power supplies in the two devices have a common ground (or technically a common rail, but a common ground makes life simpler) then one of the first two options may be the best.

If the power supplies need to be isolated from each other, then one of the latter two options may be used.

Along with that "small current" you want to detect, there needs to be some amount of voltage. Depending on how much of either you have, the selection may be driven one way or the other.

You may also require more than just the component listed, depending on the form of the signal you wish to detect and the nature of the circuit you need to drive.