Technically you're right, but this is a problem that comes up a lot in wireless home automation. Thing is, what is the attack vector you want to protect against

Technically you're right, but this is a problem that comes up a lot in wireless home automation. Thing is, what is the attack vector you want to protect against? How many burglars are going to be sitting outside your house (I'm imagining: in a black van with 'Bob's plumbing' written on the outside) analyzing RF patterns when someone comes in, reverse engineer it, then burglarize you home? My estimate is 0, even when not weighed against the alternative: if someone really thinks your house is so interesting so as to warrant several hours of waiting/observation, they'll just put a knife to your wife's throat and say 'turn off the alarm and show us the valuables'. The vast majority of garage door openers out there use unencoded RF tech, and it's very seldom a problem. And the other side: there was a recent string of thefts of BMW and VW cars in my area. Reason? They had an inside man at the main office who slipped them copies of the remotes. The tech is very, very rarely the weak link.