Odd key fob behavior - 2008 xc70

[Volvadmirer]

The one and only key fob I have has been working fine. Now, none of the buttons will work -- most of the time. Once in a while, buttons will work after car was just turned off. I've been getting in the car with the removable key. The fob always works enough for the alarm to shut off or the car to start. I would thing this is a dead key fob battery, but what I read is that the fob transponder must be working to start the car. What am I missing?

[Dzy]

You need to change the battery for the key fob and buttons should work.
On the other hand the transponder for immobilizer is not dependent on key fob battery, that`s why you can start the car. It receives enough electricity to operate through electrical field which is generated when the key is inserted in the lock and initiates secret key exchange between the lock and the key. It would be very inconvenient if you couldn`t start the car because your key fob battery is dead.