I'm living in a rented house, and I try to avoid any permanent modifications, including the entrance door, for example, installing a better lock, so I decided to build a cheap solution to immobilize the deadbolt latch from inside. There are many options in the market applying similar principle, but I have no access to those commercial solutions in this part of the world. My suggested approach consists of a piece of wood that have a notch in it to immobilize the latch in the locked position, and a small piece of flat iron to hang the piece of wood from the latch.
Also, as a bonus I included some pictures of a faster, cheaper and uglier way of getting similar results, just with a roughly cut piece of wood, two nails and a piece of wire.
Step 1: Measure the Latch, and the Distance to the Sides
This contraption works to prevent the latch to be moved from the locked position, for this you need to shape a piece of wood that will fit close to the molding or relief at either side of the latch, I have seen commercial models that use the gap or space between the door and the door frame, but in this case that space is concealed by a molding, as you can see in the pictures above. I'm not including too many measurements, since there are different shapes of latches, and this door in particular, I don't think its standard.
Step 2: Cut the Piece of Wood to Fit the Space Between the Molding and Relief
Nothing special here, just measure and make sure your cut is as straight as you can get it, with the tools you have at hand, I measure several times and used a good square and a sharp saw.
Step 3: Measure the Position of the Latch
Lock the deadbolt in the closed position, in this model, it was straight up.
Measure the position and draw the shape of the latch, this one has a diamond like form.
Step 4: Shape the Hole for the Latch
Cut the hole, as mentioned before, this cheap lock has a diamond shaped latch, there are many other handle shapes so you will have to form the hole accordingly.
To get close to the final shape, I cut several holes with different size bits, followed by a clean up with sharp chisels, and some sandpaper for the refining touches.
The hole has to be about 5-6 mm longer in the long axis to allow the piece of wood to move up and down and allow to be positioned on the latch, after a "support" of flat metal is attached to the back of the wood. The piece of metal resting against the back of the latch, will prevent the piece of wood from being bumped out of the latch if somebody kicks the door. Keep reading for instructions about the back plate.
Step 5: Cut the Back Support
The idea of the piece of metal is to act as a "rest" or back support at the back of the wood piece, like one of those serrated hangers used for hanging pictures. Actually, if you have one of those, just flatten it, test fit, and attach to the back of the wood piece, if not, follow the step below:
Measure and cut a piece of flat steel or sturdy plastic, I used a flat bar about 1 mm thick because it was what i have at hand. It is not going to be subject to any big load, as explained earlier, it will act just like a picture hanger, this piece of steel will rest on the back of the latch, the latch acting like a screw in the wall, if we use the picture hanger analogy.
Cut the backplate with a suitable tool, like a hacksaw, Dremmel or grinder.
The one I prepared it's about 5 cm by 2,5 cm (for those metric impaired, its about 2 by 1 inches)
Refine the edges with sandpaper or a grinder or whatever you have at hand. If using power tools remember that eyes and fingers, don't grow again. (Don't use gloves close to rotary tools, and a pair of safety googles costs much less than a visit to the ophthalmologist.)
Step 6: Adjust the Position of the Back Plate
With the back plate cut, use some tape to attach it to the back of the wood piece, in order to test the position of the plate, this test fit will allow to get the ideal position of the plate.
Step 7: Drill the Holes on the Back Plate
Measure the position of the two screws, about 6 mm from each side. ( For those people that suffer from metric impairment: 1/4 of an inch from each end).
Center punch the hole positions. Drill the two holes, in this case about 4 mm, and countersink with a larger bit or an appropriate countersink bit
Step 8: Attach the Back Plate in Its Final Position
Permanently attach the plate with the two screws, in the position determined previously.
Step 9: Final Product.
Here are some pictures showing the final product in position. it works very well.
This was specifically for the door depicted, however I'm sure these steps will spark some ideas in the audience for different door configurations.
Step 10: Bonus Track, the Quick and Dirty.
Here are some pictures of a very fast way of obtaining similar results:
Cut the piece of wood to the width of the space between the molding and the relief
Cut a notch in the piece of wood about the width of the latch.
Attach two small nails on each side.
Use a piece of wire or string attached to both nails, to hang the piece of wood from the latch.