Weight sensors in the bed had been tried, but they didn’t activate until the patient had left the bed, and they didn’t protect a patient who was sitting in a wheelchair either. So we hit on the idea of a battery-powered tilt sensor that would be worn in the thigh, and would sound an alarm as soon as the femur (thigh bone) angled downward more than 30 degrees.
I built a crude prototype with Radio Shack parts in a plastic box with an elastic strap to hold it on the thigh. It looked promising so we had a PCB and molded case professionally designed, and eventually received a patent. The Ambularm made a distinctive bell-like sound that brought a nurse running before the patient got to his/her feet, and fall rates were cut in half. I wasn’t involved in the later stages, but apparently the Ambularm stayed on the market until 2015.