Pressure Pad

How to build a platform for reverse pressure?

I'd like your help to build a platform for reverse pressure. Basically, I want to build a device that emits an alarm whenever the pressure is removed from a pad. Any advice would be greatly appreciated Sorry for not including details - I'm far of an engineer. I am looking for anything electrical or electronic - not sure what the difference is. It would be necessary to "alert" if 10 pounds was removed from the pad.

Want to mechanical, electrical or electronic? Basically, do the same as for a positive pressure pad, except how to take the readings. give information on the type and approximate weight of what you're looking at the track (we're talking about cars or a diamond?)

Pressure Pad

Pressure Pad