This is a product that I have used for years now. Its a simple idea. Its a wedge.
This one in particular is a big, robust, saftey asset for inward opening doors. Made by the great guys at www.sog.net, The black one has spikes on the bottom side. Close your door, kick the wedge in, and the spikes grip the floor so the door cannot be opened. To get the door open with this wedge properly kicked into place is a major chore. It cannot be done easily or quietly. Even if someone picked the locks on your deadbolt, this would really slow them down if not stop them completely. Very simple and easy to use, and very affordable as they last many years. My wedge has lasted 6 years now under heavy use and abuse of testing over and over.
Buy this wedge and use it on all of your doors at night or when you leave your home.
The blue wedge is the same, but with no spikes on it. Easier on nice floors.
I highly recommend using these. They are so simple and cheap, that there is no reason not to use them.
I have a complete video of them and how to use them coming very soon.
The guys at SOG really know there business. They do this for a living.