It's hard to solve the problem of false positives when the decision to sound an alarm is reliant on a single sensor that may start to become detached (e.g. glue/tape failure). If you think the solution is multiple sensors, well, what happens when one sensor indicates an alarm condition and the other doesn't? Now you have another potential false positive. Not to mention it's untenable to connect twice as many leads to a patient.
If they’d use three sensors, they could vote. If one sensor often votes differently from the other two, it could be marked as defective and replaced or re-seated.
Three times as many leads would be pretty annoying, though.
That could partially be addressed by making the sensor include the concept of not working. Run a small electric current across the sensor, if that current fails the sensor knows that it's not monitoring and can report it as a loose sensor rather than as a failure of whatever it's supposed to be sensing.
