The airbag sensors require power, and would, perhaps only eventually, drain the battery. I use a bluetooth adapter on my OBDII port and I suspect this very small device drained my battery after a couple weeks of not using the car. It would be unacceptable for cars to come off the production line that way.
The ADXL78 series [1] which is recommended for vehicle collision sensing draws 1.3 mA. If it were the only load, it would take on the order of ten years to discharge a car battery, which is well below the self-discharge limitations. I don't know if lower power sensors are available, or if some rule like "enabled for 24 hours after the car is run" would be appropriate, but lack of power for the sensor does not seem like a good reason for the airbags to be disabled.
Bluetooth devices actively searching for devices to pair with could plausibly draw significantly more power than that.
> if some rule like "enabled for 24 hours after the car is run" would be appropriate
There are pressure sensors, such as those used to determine if the passenger airbag should be enabled/disabled. That should be the reference for both driver and passenger; if seat = occupied, trigger airbag if collision detected, regardless of engine status, ignition switch position, etc
If only automakers could update this sort of logic over the air...
I don't think any car lasts more than a couple of weeks without being turned on, OBDII bluetooth dongle or not
For the airbag I think the sensors are passive, but even if they aren't, a grace period could be added (like, it will shut down after someone shuts off the car, then opens and closes the door)
