Keyless entry problem

[Celicasx-r]

I have this problem with my keyless entry for my 99, 6 gen where the car regularly doesn't register me pressing the unlock botton. Sometimes it will unlock first press but on most occasions it will take multiple presses for the car to unlock. The red light, lights up everytime I press it and I have replaced the key Battery 3 times. The first time it worked instantly for a bit then went back to being useless and the other two times nothing changed. I have the security on, and those who know my gen celica, it makes a sound when you lock/unlock it. I've noticed that half the time I unlock it, it makes the sound and the other half trys to but is very faint and has a lower note sounding dead. It also skips the beeping sound sometimes, meaning when I unlock it there is supposed to be two beeps but sometimes it will only do one. I don't think it has anything to do with the Battery because the rest of the electricals in the car work great. I belive this problem has something to do with the locking device in the car but before I replace it I was wondering if someone had any ideas or knowledge 

Thanks