Passenger Seat belt / Airbag Question

Hello all, I'm new to this forum. My wife and I have a 2009 Corolla LE, ~55k miles. The interior and exterior are well taken care of. Within the last two weeks, the passenger seat belt and airbag lights have been illuminating and had to buckle the seat belt to keep the warning chime from going off. This is happening despite no passenger being in the seat or objects placed there. We removed the seat cover to see if this was playing interference, but that didn't solve the problem. My next step is to disconnect the battery for several minutes to see if it resets the warning system. I've checked the connections underneath and they seem okay. I wanted to get some ideas to see if it could be a bad sensor or something. I'm trying my last resorts before taking out the seat or going to the dealer. Thank you!