http://media.ccc.de/browse/congress/2014/31c3_-_6462_-_en_-_saal_2_-_201412292245_-_megacode_to_facility_gates_-_kevin_redon.html

How do garage gate remotes work?
It turns out the ones from MegaCode simply send a individual fixed code.
And with little efforts if was possibly to clone them, send arbitrary codes, and record them all.

Kévin Redon