I don't think that'll be very easy to use. I'm not sure what sort of circuit garage door openers use but it looks like both sides need power and it may not simply close a relay. It would be taking a chance unless you could get a wiring diagram.
If you need to provide momentary DC power or relay closure these Radio Shack units are great (as are the older big black models)...
one is a monster in a box and one is a grave pop up. both currently on motion sensors and washing machine solenoids to activate them. looking for a more accurate way to activate as these sensors are so hit and miss.
When you say motion sensors are you talking about the ones from security lights that are simply switching AC? Those should work pretty well but can depend on the setup and environment. You may be able to improve the performance of your motion sensors by making a snoot. It's basically a tube mounted to the sensor body that restricts it's field of view. They become much more controllable and reliable with this configuration. You can point them where people will walk by and they won't trigger on movement away from that spot.
Since you're using the solenoids with no prop controller the electric eye won't work out of the box because most of them have an instant on and off as the beam is broken and then cleared. You'd need a time delay relay (which are easy to use and work great) or a prop controller/timer circuit.
I think the "snoot" he is reffering to is just a cone attached to the body of the sensor, think of it like a sno cone cup, cut off the bottom and attach the big end to the sensor, make sure it completly covers the sensor.
you could just experiment with some construction paper, if it works well for you.. id personally look for some thin plastic type sheeting.. like the dividers they use in school binders.
The snoot is just a tube attached to the sensor body (not the sensor itself). An easy material to use is black construction paper. Tape an edge to the sensor body and then fold/wrap it around the rest to form the tube. Add more tape once it's complete (mine are completely covered in gaffers tape) and it'll be reusable and weatherproof as well.
I'll try and locate a picture of mine from last year or post a new picture once I have them unpacked.
hook it up to a levelite universal controller and it will work seen one on ebay it will almost work any trigger .....pressure switch.........anything from 120v...to 5 to24 vdc it was on ebay for 18 dollars