Q:

Fixing car key when rubber buttons fall off

I have an old car key and the rubber buttons that push the micro switches have come off.
How can I fix this to make the car key usable if I still have the rubber buttons? What about if I don't still have the rubber buttons? I don't want to spend lots of money as the car is old and might not last long. 
UPDATE:
So while my original question specifically related to micro-switches upon reading the hack on the Sugru site how would the key be fixed if the "small rod that touches the chip" was missing?

A:

Use Sugru to fashion new buttons. I've made everything from phone cases to hinges for my car's sun visor from that stuff. It is holding my shoes together.
The problem with the car keys is the waterproof aspect: you don't need any rain getting into the electronics as they not only unlock your door remotely, but they also (assuming that is a Renault key as it looks like) may perform an electronic authentication with the car. Sugru is waterproof, and it is flexible enough to act as a pushbutton. Since you have the old buttons, just smear some Sugru over the old buttons to create a new waterproof surface that will hold the buttons in place.

A:

OK, I have solved my issue - I had both of the buttons still - I covered the buttons with clear tape.

Would still like to have some 'hacks' in the case the buttons are lost. I almost lost them a couple of times before I put the tape on.  

A:

I ran into this problem with one of my Jeep key fobs. The rubber buttons wore out, and popped off.
I fixed it by reinforcing the rubber membrane on the inside of the fob with liquid electrical tape and then super gluing the buttons onto the liquid electrical tape. I did this hack over a year ago, and it still works great.
The steps I took were to open the key fob, and remove the rubber membrane from the inside of the fob. Put the plastic case aside, and tape the loose buttons in place to the membrane from the front to hold them in the proper position. Then I layered on several thin coats of the liquid electrical tape on the back of the membrane until it built up a good thickness. After that was all dry, then remove the tape and gently peel off the buttons. There should now be a perfect impression in the rubber membrane where the buttons were. User super glue and permanently glue the buttons on. Reassemble the whole fob, and it will be just like new.

