My bedroom light is controlled by only one switch (as far as I'm aware of...), so I assumed my switch would only have 3 wires (current in, current out, ground). However I opened my switch and I saw 4 wires (see picture below). What is the 4th wire for?
UPDATE: If I reverse the two "push to release" wires, this switch seems to end up turning on/off a completely other switch in my bathroom. For example, after reversing the wires, in order to put on my bathroom light, I have to put on this light. So I guess this switch is connected to my bathroom somehow, and that is related to the 4th wire. But why, and how?
BTW, I am asking all of these question because I want to install a dimmer switch.