Is there a device that can be used in a restraint-free facility that alerts staff or residents that MIL is about to fall from her wheelchair?

My 95 yo MIL lives in a restraint-free facility. Her mobility is limited due to age and a fractured femur several years ago. She spends much of her time in her wheelchair. She is able to transfer from chair to bed and chair to toilet. The problem is that recently she has been falling asleep or losing consciousness and falling from the chair. (This has happened at least 3 times in the last month). After her most recent fall the staff has taken away her wheelchair and she must have staff present to use it. Since she has been using the chair to get herself to the bathroom, to get to her closet for her clothes, to get to meals, and to get to activities her independence has been severely curtailed.

Is there any kind of alarm or appliance that is not considered a restraint that would alert her or the staff when she has slumped so far over in the chair that she is in danger of falling out?