This hefty piece is somewhat less portable, but offers a significant security upgrade to any strike-plate equipped regular door with a knob, and attaches in minutes. This is the Strike Plate Lock.
The principle of the lock is to replace the existing strike plate with a hinged plate, attached to a heavy-duty chain and a ring, which loops over the door-knob, providing a frame-mounted, door-knob fixed physical restraint to your door.
The metal is 16 gauge 300 series stainless steel and 0.050" thick the ring is 2.5" inside round and 1/4" thick. It affixes to the frame using the existing strike plate screw-holes, and two long screws came along with it.
I used my multitool, undid the old screws and removed the old plate, and attached the new one in less than two minutes, and immediately bolstered the effectiveness of my front door.
I wondered how much the latch and facing would be exposed and whilst you can see both strike-plate, latch plate and the chain are visible, the door is only open a crack, and there is no easy bolt-cutter access to the chain, just a nice balistraria for me to fend off invading triffids and zombies.
The creator, Robert Dieguez, gave it a very thorough workout, in the video I pulled from his site, below:
I didn't want to put my (rental) houses' front door through this kind of test, so I'm glad that Robert did so with his testing-frame. I was pleased to note that the whole rig seemed to slide itself out of the way either due to good design, or just how my screws alignment shifted the center of balance, but when not in use, it folds out of the way, and when in-use, I have a very secure additional feature to home security.It was a fast, easy and unobtrusive addition, and appears to be outperforming other chains and door-bolts.
Go check out his Kickstarter, the webpage and Facebook .
[EDIT] prototype proof video