System Definition:

I submit that you may require the system to report as soon as the ignition is turned on since that is when most status sensors report in. This would be consistent with the idea of warning them of a flat tire before rolling over it and weakening its structure further.

To do this, you'd need to quickly define your communications link which affects the power profile. Your kinetic motor now would be used to maintain a charge on a super cap from which the system extracts power.

Communications is key because the device might need enough power to "listen" for a request to power up, measure, and transmit before powering down again.

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That given, I'm directed to using an RFID technique to beam energy into the wheel monitor. No kinetics would be required making retrofitting or installation easier. You need RF to get the telemetry out... why not use the same RF to draw power?

The pressure sensor... I'd research MEMs technology. Lowest power, smallest mass.

-Jay C. Box