Open it again, remove the battery and with the vacuum cleaner on blow dust it that way replace the battery and see if that helps.
If not replace the battery with a new fresh one and if the battery you used is new, take it back or try on something else like a remote control etc
Chetak
If it keeps going off it's not a battery problem the senor is probably telling you some alarms have and some don't can recognized carbon moxi an over heated appliance or a burnt or shor in a wire. Obvious you have all ready checked for is no fire I asking you not to take out the batteries to keep it from going off but double check every thing.
Hello
If it one that you open try putting a vacuum cleaner up to it. If that doesn't work try a Hair dryer on cold.
On most there is a little box with a light at one end and a photo sensitive cell at the other end. Smoke interrupts the light which sets off the alarm
Andy C
Hi it can detect other chemicals in the atmosphere.
Because I beleive the battery is new and there is no smoke or anything.
