I don't think placing the mats on top of the mattress would pass the "Princess and the Pea" test, but equally the weight of the mattress alone would probably trigger the pressure mat anyway. Which is probably why I haven't tried it yet.

I have also considered strain gauges on the slats ... a little more work involved, but could have some interesting applications if an analog value is supplied to Cortex. Eg: Over a certain threshold Cortex announces "no butter on your toast this morning, fatty". Or maybe sets the alarm earlier to ensure sufficient time to cycle to work instead of drive. That would be my side of the bed, obviously ....