If using a key, you must leave the key in the lock at night when people are home. If the key is not obvious, you will not get out. Fire survives on oxygen. While if is burning in your home, it can and will deprive it's occupants of the necessary oxygen to sustain life. You become incoherent to your surroundings and can't find a way out.
Flood lights are an excellent deterrent.
Go to home depot and buy a motion-sensing floodlight. It's a proven fact that a house that looks lived in is less likely to be burglarized. By leaving interior lights, stereo, or a television on, you give your home the advantage of looking lived in. As a security professional and firefighter, it distresses me to see how lackadaisical people are when it comes to fire. It saddens me to see death and destruction, where death and destruction could have been avoided.