When we bought our garage door opener, it came with two remotes. It was enough for 2 people but not for three(and that third person would be me). It became a little annoying after a while, having to unlock the rear door and opening the garage door from the inside, so I decide that it was time for me to do something about it..
Step 1: Materials
All you need for adding an extra remote is a set of paired transmitter and receiver (well, obviously you'll also need some other materials, such as some wire, solder, a soldering iron, and some other utility tools). You might also need a power source for your receiver, like a wall wart.
Before beginning, you may also want to check your transmitter and receiver to see if they work.
Step 2: 2 Ways
There are many different ways to adding an extra remote to your garage door and I'll be showing two ways. The first way would be to simply connect the receiver at the switch that controls the garage door. This is an easier approach (no need to climb up ladders and work over your head), but you need to find a power supply for the receiver. For the second way, you will also connect the receiver to the switch; it will be connected in the garage door opener. This approach will allow you to use the power from the garage door opener to power your receiver.
Step 3: First Approach
The first approach is to connect the receiver to the garage door opener switch at where it is. This should be easy. First, remove the switch from the wall and expose its contacts. Connect one of the contacts to the COM (common) terminal and the other to the N.O. (normally open) terminal of the receiver. Secure the switch back onto the wall and find a way to power the receiver, most likely by using a wall wart.
Step 4: Second Approach
The second approach will most likely require you to climb ladders. Be careful. First, unplug the garage door opener, then remove the covers. Find the contacts were the the switch of the garage door opener is connected, and like before, connect one of the contacts to the COM (common) terminal and the other to the N.O. (normally open) terminal of the receiver. After doing so, you'll have to somehow power your receiver. This can usually be done by using the power source from the original receiver of the garage door opener.
To do this, plug the garage door opener back in (you'll have to be very careful now because this introduces live power) and using a multimeter, find an appropriate power source and connect your receiver to it.
Secure the receiver, put the covers back on and test it!