A smoke alarm is a warning device that detects smoke at the earliest stages of a fire ......
Smoke alarms are cheap at less than £5 and available in DIY stores and at many supermarkets. 
Buy a smoke alarm with a 'hush button', then you can stop it if it goes off by mistake.

Where should I put my smoke alarm?
Always make sure they are fitted in accordance with the instructions provided.  The more alarms you have around your home the safer you, and your family, will be.
Fit smoke alarms on each floor level in your home.
All smoke alarms should be mounted on the ceiling and should be at least 30cm away from any wall or light.
Don't put a smoke alarm in the kitchen where it can be set off accidentally.  Put it out in the hallway.

How many should I have?
The more you have the safer you'll be.  At minimum you should have one on each floor - probably in the hall and landing ceilings.
But if you have only one smoke alarm and two floors, put it where you can hear it when you're asleep - in the ceiling at the top of the stairs leading to the bedrooms.
If you have a TV or other large electrical appliance in your bedroom, you should fit a smoke alarm there.

How should I Look After my Smoke Alarm?

1. Once a year Change the battery in the alarm (unless it is a 10 year alarm)
2. Once a week  Check the alarm by pressing the test button
3. Once a month  Vacuum and wipe the smoke alarm casing to ensure dust isn't blocking the sensor chamber (For mains wired alarms, switch off first)

It keeps going off
If your smoke alarm keeps going off don't take out the battery!
The problem is easily solved.
Most probably it is positioned too near the kitchen. Move it further down the hall.
If it is not the cooking setting it off, try vacuuming the alarm as there may be a build-up of dust or dirt.