Andrew wrote:

Mobile phones modulate their output power to the lowest level
needed for communication. I believe this is why you should not
use your phone in a plane, because it tries maximum power.

Do smart meters carry out this same process ?.

Smart meters will use off-the-shelf transceiver modules (zigbee,
wireless-mbus, sigfox, etc) which will use ISM frequencies at permitted
power levels, if your stairlift can't cope with sharing the bandwidth
with other devices, it's the stairlift's fault ...