The alarm is hot and smells?
Joking aside there could be a fire risk, Turn off the mains, by the spur of the main consumer unit. Then open the panel and put in your code to silence it, then remove the battery. Your external sounder may ring. Just clsoe the panel back up and turn on the mains again and then enter your code all should be fine.
Tahe the battery to a local suppliers and get another, do the same with the panel and relace the battery correctly and then thats it.
If unsure get in a professional use a NACOSS or SSAIB company.
Alarm
September 2011