After I logged into the cart (by using a hidden unlabeled scanner on the underside of the cart that the attendant had to show me,) the screen instructed me that it was a good time to load my own bags into the cart, if I had brought any. I dutifully started arranging my bags in the cart; it gave me seemingly about 30 seconds to do so before it started screaming at me and demanding to know what I had removed from the cart. This was a particularly shitty experience because the screen is angled in a way that it is not visible unless you are standing in the back of the cart, but the sensor package is too large to be convenient to reach over; you have to scan and load each item from the front or side of the cart, and then walk around to the back to be able to see if it worked.