Key and locks not communicating

[bmsamson]

So I'm having an issue, wonder if anyone out here has had and solved it and can point me in the right direction. 1/my car is an 03 base manual, around 140k miles. 2/the key is less than 2 years old, real P part not ebay special. worked fine since delivered. 3/Recently, the key wasn't working, no red light, so i replaced the battery 4/now I have a light, but it doesn't seem to 'talk' to the car's locking/alarm system. nothing works when i hit any of the buttons (but the light does go on). 5/yes, the car still starts and runs fine 6/when i use the key in the door it locks and the alarm light on the dash does start flashing, and unlocks/deactivates the alarm from the door as well.

It's a real pain to have to open the trunk/frunk from inside, use the key to lock unlock, etc. I'd really like to get this sorted out. Any suggestions greatly appreciated.