Exactly.You're suggesting the workaround is to never let the car go to sleep to maintain the working state of the sensor. Instead of just enabling sentry mode at home, can't that be done more thoroughly by just disabling it from sleeping? I'm not near my X, but in my S and 3, I recall there was an option (in the display menu???) to keep the car awake at all times for immediate app connection or something.
Just checked my X and Y, didn't find obvious options to disable the car from going to sleep. Perhaps in older versions or 3rd party app?