The Flip Guard from Ultimate Lock System is a great device if you want added security for your deadbolts!
This one is mounted on the back door leading into our garage. Once both cars are in the garage and we are inside the home, we flip the guard to securely lock the deadbolt so that nobody can get inside even with a key! When we leave the home, we pull the latch down so that the deadbolt works as normal.
Paranoid? Perhaps, but having worked in law enforcement in the past, I know that you cannot have too much security. I HIGHLY RECOMMEND THIS DEVICE for anyone who is security conscious. If you simply search "Lock Bumping" or "Bump Key" on YouTube, you'll be shocked at how easy it is for an intruder to enter your home. With this device on your deadbolt, they can't bump the lock to get in.
Installation is extremely easy... just loosen the deadbolt by unscrewing the two screws that hold your deadbolt in place and slip the flip guard behind the lock. Then tighten the screws and you are done! I decided to slide the Flip Guard further in so that the flip mechanism is centered to the deadbolt lever. I think they make it a bit larger so that it can fit any type of deadbolt. Also, be sure to position it so that the guard flips down when open. This way, it can't accidentally flip into the lock position when you are outside of the home which would lock you out! There's really no way it would happen even if you did mount it wrong as the flip handle is tight enough that it does not swing open or closed by itself anyway.
This device is used to keep you safe while you are INSIDE your home. It doesn't do any extra protection for you when you are outside the home since it doesn't engage when you leave. You can only engage it when you are inside. Still, it's one added safety for you to protect you from home invasions.
I have an Amazon link for you in case you have an interest in this device. I chose the satin nickel finish as it matches our hardware better, but there are other finishes available.