On 14/07/2018 20:02, Harry Bloomfield wrote:
Dave Plowman (News) was thinking very hard :
Keyless entry - such an essential thing to have ;-) - transmits all the
time. When the transmitter is in range the car opens. I assume these code
readers are somewhat more sensitive than the receiver in the car.

If you are suggesting that the key transmits all the time, think about
it and how much battery that might need. They transmit, or more
correctly respond only when intergated by the car.

The car transmits all the time and the key responds when it receives a
request from the car, so little power drain.

Normally the fob muust be pretty close to the car and it might well be
possible to power it from the signal it receives.

SteveW