Does such a product exist that can be retro-fitted to a van (2002 Citroen
Relay to be precise), whereby it would have the functionality of slam-locks,
but would have an emergency unlock feature (somehow connected to
impact/inertia sensors?) whereby the doors would unlock in the event of an
accident?

Any links/details and rough idea of prices would be much appreciated.

Cheers,

Peter
-- 
"Doctor Fox was on the panel and I asked him why we didn't even get
nominated, and he said 'because you're not very good'. <pause> At least I
don't practise medicine without a license." - Ricky Gervais on the Sony
Radio Awards