Portable Door Lock.Solid Brass.Stainless Steel. Made USA-Calslock

This two-piece steel (brass-colored) "Portable Door Lock" design has been around for many years. The Calslock improves on the previous design with a wider piece holding aginst the door, but it still has a couple of the same limitations as previous versions. This makes it only suitable to prevent someone "casually" trying to open the door, not a determined break-in with some force on the door. The current Jan. 2023 price ($34) is also a bit high for what it is (just three pieces of formed spring steel).The lock has a D-shaped spring piece that adjusts to the door width by fitting into small teeth along the slider piece. When the L-shaped piece on the end of the toothed slider piece is hooked into the strike plate hole, you close the door and can then squeeze and adjust the D-spring so that the peice blocking the door from opening rests up against the door. When someone then tries to push in the door, the lock is supposed to be held in place by the D-spring resting against the slider teeth and the L-shaped piece pressing against the back surface of the strike hole. In concept, this would prevent the door from opening. Unfortunately there are a couple of limitations.1. Door-stike plate gap:The lock only really works on doors where the distance between the door and the strike plate is small - so be sure to measure what you have. Because the width of the steel slider piece is only about 1/16", the gap between the door edge and the strike plate can't be much larger than this. If it is much larger, when the dead bolt is disengaged and the door pushed in just a bit, the Calslock will angle to one side, and then a more forceful push against the door can cause the lock to bend and just fall off. Many doors don't fit so well, and often have a gap up to 3/16" - if it is that wide the lock probably won't work. Obviously if the dead bolt is engaged through the strike plate, the lock won't fall off like this, but in that case the travel lock is only reinforcing the dead bolt a very small amount and really isn't needed - the deadbolt is obviously much stronger by itself.Also, the L-shaped end of the slider that hooks into the strike plate hole is short, which contributes to the problem of it angling with a hard push. Unfortunately a lot of travel locks have a similar limitation.2. Strength: Two issues here. While it is quite rigid, the 1/16" steel of the slider and spring are really inadequate to prevent someone like a large, heavy man ramming his shoulder hard into the outside door. It is only going to prevent someone from casually trying to open the door. As I mentioned, the L-shaped piece on the end of the toothed slider is short, which also reduces strength against a determined push-in. It should be a bit longer for more stregth, since most strike plate holes in the frame or box strike are deeper than this length. Lastly, the teeth on the slider should be deeper and the U-spring need should be stiffer, because a determined hard push-in can just cause the U-spring to disengage from the teeth and be pushed back, causing the lock to fall off.Unfortunately, except for one much more expensive travel door lock that uses padded adjustable screws on both the door and casing, most of the inexpensive travel door locks aren't very strong and will just slow down a determined person from pushing in the door (there are several models with lots of reviews on Amazon). For under $30, the current version of the old-fashioned long rod that jams between the underside of the doorknob and the floor may be better than most, or you can use that type of rod along with another of the inexpensive locks together for more protection. With the rod, you just have to adjust it correctly and jam it in well. Using the rod and another lock will may slow someone down enough for you to become aware of the attempted break-in and take action to protect yourself.