"Larry Dighera" wrote:

I don't think the transponders actually check for warmth.

A transponder contains what is termed a Crystal Oven. This is a
small
chamber in which there is a heating element and a quartz crystal
used
to determine the transponder's transmission frequency.

Which brands/models have that feature?? The frequency accuracy
required by the TSO can be and is achieved without a crystal oven.

The built-in turn-on delay is merely to allow the high-voltage
supply to come up to full volts, and the cavity tube filament to
heat up.

Fred F.