Yaris t-sport 2005 key fob not working

[MrSkeedle]

Recently my key has started playing up on my 2005 yaris t sport. shown is a picture of the type of key i have. Basically ill go to my car in the morning, click unlock and it just does nothing, the light on the key lights up but the car doesnt respond at all. I walked around the car everything, pressed it a hundred times and nothing. i have to unlock manually, in turn setting the alarm off. when i put the key into the ignition the alarm DOES NOT stop going off which i find very strange. about 30 seconds ish later, the alarm finally stops sounding and the little red light near the handbrake stays on showing the system is like still armed i suppose? Once ive driven the car and take the key out the alarm usually goes off again, but now the key is working fine and unlocks, stopping the alarm. i can then lock the car as usual. Later on in the day when i come out of work, its still fine. even the next morning it might be, but then a couple days later, here we go again. I've put a new Battery in the key, but the package looked a bit old, yet still sealed. ive ordered a 100% brand new duracell one, just in case. but it looks like the Battery is not the issue. its like the key and car are losing pair? The thing that is really confusing me is that when the alarm goes off and i put the key into the ignition, the alarm continues to sound. the immobiliser is working surely, as the car starts. Any ideas would be much appreciated thanks everyone. 

[Stivino]

Get a new Battery, a decent branded one.  Pop it in and see how it goes.

The light in the fob will light up even if there's not enough power in the Battery to signal the car to open.

[MrSkeedle]

4 minutes ago, Stivino said:

Get a new battery, a decent branded one.  Pop it in and see how it goes.

The light in the fob will light up even if there's not enough power in the battery to signal the car to open.

Yeah, got a duracell one coming from Amazon tomorrow. ill see how it goes. but it does all point to low key Battery doesnt it? but i did already put a brand new panasonic one in and it made no difference. but i dont know the age of that Battery, it was in the car from the previous owner who told me about it. but who knows it could have been there for years. thanks for the advice!

[Gooner20112012]

Do you have just the one key?I have 54plate yaris and i have 3 keys. When i had to replace Battery i had to reprogramme key fob.