Weird key fob behavior

Hi,

My car came with a key fob and then a backup standard key (no fob).

I have been using the fob for around two years with no issues. Then about six weeks ago it would not unlock the car. So I presumed it was the battery and bought a new one. No luck!

On nine days out of ten, the key does not work to unlock the car. So I have to use the key in the door and the start it quickly before the alarm goes off.

Then, when I turn the ignition off it does not lock either using the key fob. However, if you put the key back in and click the key round (don't actually start it), turn it back off and take the key out, the key fob will work to lock it.

Any suggestions on possible fixes? Would ideally fix myself if possible.

Thanks in advance!