Do you have a key fob with a battery? little light on it? When you change the battery you have to go through a little process...
Let me know if it's a key with battery and one little button.. and the battery might need replacing..
I'll give you the procedure from the owner's manual...406 page 108.
PAGE 108 translation form Dutch language 406 Owner's manual:
(comments in Parenthesis are mine)
(Button A is big and is the Peugeot symbol)
(lamp B is southwest of the button A)
If little lamp B only lights once or never lights at all if button A is pressed, change the battery.
Pry the housing off with a coin and change with battery CR 2016 / 3 volt.
If the remote control doesn't work after changing the battery, it must be re-programmed.
PROGRAMMING the REMOTE:
- Press on button A until the lamp B no longer blinks.
-Let the button go, the lamp should light constantly.
- Press 2 times on the button in the immediate vicinity of the auto.
- turn the ignition contact ON for at least 3 seconds
- turn the ignition contact OFF.
the remote control now works again.
Consult a Peugeot dealer if the problem persists.