Don you are correct it will still be on and working. Fortunately even under those conditions the batteries last for a very long time if they are fresh.
While you make a great point and logically we should be able to turn them off if we want to, I don’t think any of the sensors have some sort of on board on off switch.
Honestly I don’t think it would save much battery, I am fairly sure they use as much power wether detecting motions or not. Only way to save battery power would to be turning it off completely but then there would be no way to turn it back on remotely And being Wireless is the kind it’s thing