It isn't the weight, it happens with many devices in Gen 1 cars as well.I was driving alone with my siren red Chevy Volt 2017. I connected my iPhone 7, and then just threw it into the passenger seat. After driving a few feet, I heard bong-bong-bong, then I looked at the dash, there were no messages there. So I was suspecting it was the latest recall service that I did yesterday. Then after I got into a stop sign, made a right turn, then bong-bong-bong sound came on again. This got me worried and drove on. Then after some time, I noticed a glowing red light on the overhead where OnStar area is. My golly, it says that the passenger airbag is on and my passenger has no seat belt! So I grabbed the iPhone and placed it under the DIC, and the growing red light turned off. An iPhone 7 needed a seat belt? Really?
Well, anyway, I tried different spots on the passenger seat, and yes, some areas won't trigger the passenger sensor while in other areas, the iPhone 7 is enough to trigger the passenger sensor!