A good habit to start, is to change your batteries when you change your clocks. In fact, don't just get one detector. Make sure you have one on every floor, especially outside the bedrooms.
Smoke detectors are available at stores everywhere.
Please, for your family's sake, pick up your smoke detectors and install them today. STOP what you are doing. DROP to the ground, cover your face with your hands, and ROLL around until the flames go out. Practice with your children. Practice your home fire drills , always have 2 ways out of each room.