Made by General Motor's European division Vauxhall, the Astra has experienced growth in popularity and comes in three different models: the Astra Twin Top, the New Astra and Astra. The Astra's older key fobs have a tendency to wear down the joint in the transponder circuit that signals the car it is OK to obey the fob's commands. In repairing your Astra key fob, you will have to repair the break in the circuit.
Slip the key and the key fob apart. This can be achieved by gently pulling them in opposite directions. On the inside lip of the key's fob, you will see a small piece of plastic that sticks out. This is the circuit for the key fob. Over time, the soldered join between this circuit and the key will wear out and break.
Look for the broken join. It will be a small dot of metal and will not be joined to the green circuit board. Take your soldering gun and using your solder, rejoin this to the circuit board.
Change the battery and replace the cover. Put the key in the lock and turn to reset the electronic signal that operates your car.
Take your remote to an automotive locksmith if these steps fail to elicit a response from your car when the buttons are pressed. A reputable automotive locksmith can repair your fob cheaper than replacement by the dealership or even online. Use a professional association such as Master Locksmiths to find a locksmith online.