Our car keys consist of a mechanical key with a tiny and very expensive transponder-chip inside. The transponder moves around freely inside the encasing, although there is a small recess where it fits into. These keys can come or break apart, and the sort with push-buttons periodically need to be taken apart to replace the lithium battery CR1616.
The tiny transponder-chip is not attached to anything, and therefore usually falls out of the key when opened. You may lose it when simply changing the battery. If it pops open unnoticed in your trouser pocket, for example carrying something large and heavy, you might not find out soon enough to salvage it. When it is gone, it will often have happened unnoticed and never to be found any more. Without it, the key is rendered useless for starting the car.
As seen in the photo, there is a little recess the transponder-chip is supposed to be put in. Add a little dab of universal glue (PU glue or similar) to the flat side, insert it into the recess, and the chip stays in place. In the picture, the chip is properly glued into its place where it should remain.
Doing this will save you a lot of money sooner or later!
I was quoted €275 for the chip plus €75 for programming it, currently being US$ 280. It makes me wonder why Mitsubishi saved less than 0.01 cent on the glue.