When An Alert Sounds
When an alarm emits a beeping sound it is for a couple of different reasons. If there is intermittent sound constantly then, depending upon the brand of alarm, it could be warning you that it has come to the end of its life and will need replacing. Check your instructions to see what is causing this sound but if the reason is that the alarm has reached the end of life then no battery change will work and will certainly need to be replaced with a new one.
This beep should sound off at around 7 years after you purchased it, so this should give you a rough idea of whether the noise is one that means you need a new alarm.
Another cause of the sound could be due to the fact the batteries need replacing. In this case, once again, check the manufacturer guidelines and install new batteries immediately. Only replace the batteries yourself if you are confident in doing so, otherwise contact a professional to have them changed and positioned correctly.
The other and most important reason is could be beeping is due to the presence of CO gas in the house. If the alarm is constantly sounding then you should realise that there could be CO gas being emitted. The first thing you should then do is open any windows and doors and evacuate the property immediately. Once you have provided ventilation to the property and made sure everyone that was inside is safe, then call the gas emergency services.
Do not re enter the property until a gas engineer has been, tested all of the fuel burning appliances in the house and made the appropriate repairs, or turned off the appliance that is at fault. Once they have given the all clear and the house has been ventilated for a long period and the CO alarm is no longer sounding, then it should be safe for you to enter your home.