I have a 2007 Mazda 3 hatchback. Today, it started beeping when I opened the driver's door. My headlights were not on. The fob would not lock or unlock the car. Luckily, I can lock the car with the key. I removed the battery from the fob for a test. The battery tests good with a high output. So, what the heck is wrong??

 

Most likely the ignition barrel is sticky & not releasing the " key in barrel" trigger. Try adding some graphite powder into the barrel & cycle the key in & out a few times. This may just save you a new barrel.