I've just been shown a simple solution sorting out HF (not IR) remote
locking / unlocking problems on your older (P, R or S reg) Peugeot 406.  My
remote was becoming more and more unreliable, sometimes would refuse to
unlock or lock the car.  Last week it died completely. Although the little
red led on the key was showing good batteries, I decided to fit new ones but
this didn't help. My local Peugeot garage wanted £60 plus for a new key and
a charge to programme it. They said it was the only solution...

A friend suggested a trick he was shown by a Peugeot Mechanic.  This is what
he suggested...

1. Unlock the car with the key and use the keypad to deactivate the
immobiliser.
2. Start the car.
3. Now press the large button on the key about 10 times, pausing briefly
between each press.
4. Switch the engine off and remove the key from the ignition.
5. Now press the large button again...  Hey Presto - doors lock and unlock
by remote again.

9 times out of 10 this will have solved the problem and your remote will
work again. How / Why??  Who knows.

Hope this is of use..