Turn it off with the special key under the bonnet (hood?) on the inside wing
left hand side. Black plastic cover sometime fitted over keyhole.
No key? Peugeot Uk wanted over 100UKP for a replacement lock and key about 8
years ago. Instead, peel back the sheath on the cable. I think it has 4 or 5
wires. Only two go to the switch, two form a tamper loop. Cut the two going
to the switch contacts. Insulate the cut ends.
Use the keyfob to clear the flashing light on the dashboard and from then on
only use the mechanical key to lock the door. Remove the batteries from the
key to make sure you don't forget and set the alarm again.

bob

Ignore the septic.

the alarm is located under the driver seat and has two large plugs,
disconnect them and forget about the alarm.