The detector is set up to operate a solenoid valve. Motorhomes of some eras had a propane shutoff valve held closed by a spring and opened by a solenoid connected to the propane detector. The idea was that, if the propane detector tripped, or was disconnected, the gas supply would be shut off. I don't think they were ever used on trailers in the U.S. but maybe they were, or still are, in Canada. Or maybe someone put in a propane detector with the extra circuit and there isn't a valve connected to it.
There were two problems with that approach. One, the solenoid valve requires enough electricity to hold open to pose a fairly serious problem for boondocking. Two, propane leaks into the living quarters of RVs have never been a notable cause of fires.
The solenoid valve setup is still used for marine applications, where propane fires and explosions have been a much more serious problem, and where battery operation for days at a time is highly unusual.