Q: how much weight is required for a seat sensor to detect someone

Occupant weight sensors (OWS) are required in new cars and they must meet the regulatory requirements of Federal Motor Vehicle Safety Standard (FMVSS) 208. To give you a common example, in Honda vehicles if the occupant weight sensor detects the weight of a child (up to 65 lbs or 29 kg), the system will automatically turn off the passenger’s front airbag. Other manufacturers’ systems are comparable although reportedly occupant weights up to 100 pounds have caused passenger air bag system de-activation. I would go with published values, though, such as that reported by Honda (65 pounds) which is probably typical. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.