Battery driven device for completeting a low voltage circuit?

Fibaro Smart implant should do the job, it should run on a 9V battery, but 9V DC is the minimum; two 9V batteries in series is probably a better idea, then it gets 18V DC with fully loaded batteries.
30V DC is the max voltage it can handle.

It has 2 potential-free outputs, with one of them you can switch your garage door.