I have a Mercury Sable and we found that my remote will open a Ford Focus in our neighborhood.
Oh, yeah! That reminds me of the time when I had an aftermarket alarm installed in my car, in the 90s I think. I was at a bar one night with a sideyard bordered with a chain-link fence. I think what happened was that I think I forgot to set the alarm, so I clicked it and it armed itself. At the same time, it disarmed another car close by as its owner was walking away from it. He armed it again, and I clicked it off. He turned around and went "Whaattt??" Armed it again. By this time, a friend was snickering at this drama, and I clicked it off again. The man was getting mad, wondering who the hell was doing this. He rearmed it and I clicked it off again one more time. Meanwhile, I was standing around minding my own business.
With my vehicles, I don't have that issue. I don't miss hearing the beeps of the alarm on a previous car. I don't have to worry about accidentally forgetting to disarm before opening the door. That car, you couldn't disarm without a sound, so when I had to get inside, everyone in the camping area would hear it. "Wake the hell up, people. It's 3 AM!! What are you doing asleep?!" Why didn't they allow for a stealth disarm/arm cycle? Ooohhh, wait a minute... That's rriiiiiight... People who drive newer CR-Vs in general don't go camping and wouldn't know what to do in the boonies.
The remotes are one reason why it would be a nice thing to be deaf. I don't have to hear alarms going off or being armed/disarmed all night. I'm surprised that as a health hazard from a lack of deep sleep, that someone hasn't initiated a petition for a law requiring that alarms be configured to allow for stealth functioning.
Naisho, I know for my Wrangler, you have to have a key that electronically matches yours for the Key Sentry system to allow it to start the motor. If the code in the keyhead doesn't match, even if the key is the same physically, it won't start (in other words, the dealer forgets to code the key before giving it to you, or you fail to follow the manual on how to program extra keys from the ignition). Of course, it doesn't stop the dedicated thieves from getting around it and stealing it anyway.