Does anyone know how these sensors work, please?

They allow the computor on the collection vehicle to record the weight
of your bin contents.
If you don't want the council to know this info then just pass a
powerful magnet over the sensor.
This is illegal of course and not to be recommended....the rubbish
police will get you somehow and theres always the possibility that the
incompetant Blair will be so miffed he might just change his little mind
again and hang on for another 9 years.

P.Pleater