Dealer says No sensor for passenger seatbelt!?

[autoque]

Since day one, the passenger seatbelt warning has never worked, like the sensor is broken. So I took it to a dealer for the problem and they say that there's no sensor in the seat but it's on the passenger side floor so when someone's seated it would know by the weight of their feet! And that's how the airbag decides if it wants to deploy or not. And there's no alarm even when not fastened. They say it's a more advanced design than a seat alarm. I really doubt their word so I'm taking it to another dealer for a second opinion. What do you think?