my chip fell out of my vauxhall astra mark4 key fob?

You have to get a new chip and get it programmed.
A used chip can't be re-programmed.
New chips are not expensive, but the programming can be, especially if you don't have the 'car pass' card with your immobiliser code on it.
Doesn't have to be done at Vauxhall, lots of places can do it.

spence
October 2010

you could but it wouldnt start

me
October 2010