Can't turn off car alarm using the car key

There is definitely something wrong if the system arms and won't disarm. If it arms with the key it should also disarm with the key. You have to determine if the alarm is factory or an aftermarket accessory. If It's a non Honda alarm then you will need to take it back to the company that installed it. There are a bunch of different companies out there that install alarms and they are all different and work in different ways. If the system is factory Honda the alarm should shut off when the vehicle is unlocked. The system will most likely have to be diagnosed by a qualified technician.

You need to have your key sync with your car, look for steps on how to do this or request help on sinautoscan.com under forum