After I bought my Glock 17 for protection, I remembered the first time I had to pull my gun as a reserve police officer. I shook like a leaf! Then, I imagined it would be the same if I encountered an intruder breaking into my home. I remember seeing cop shows on TV with laser sights and when the crook saw the laser dot on his chest, he calmed right down realizing where the bullet would hit. So, I figured I could do the same and should at least be able to put the laser dot on him – even if I was shaking.
I found this sight on an Ebay store, called Outdoor Bunker, sells for around $25 and is available in black and silver colors. (It also fits Weaver/Picatinny rails)
The package comes with the laser sight and mount made of aluminum, 3 batteries and 2 allen wrenches. Taped to the mounting is a pin which locks in on the groove under the Glock barrel. The switch is at the back of the laser barrel and is easy to turn on. It also has four adjustment screws at the outer end of the laser around the outside.
Load the batteries first by unscrewing the back. Mounting the sight is a bit of a handful steadying the gun while you tighten the allen screws. Tighten them evenly so it doesn't bind – don't overtighten! You may want to leave the center one a bit loose so you can turn the laser barrel in the mount. I suggest turning it so the switch horizontal so that you can turn in on with your index finger as shown in the photo. (That's where your finger should be anyway, until you are ready to fire). Turn on the laser and view down your open sights to see how accurate it is. Make a primary adjustment up and down by rocking the laser and mount until the height is very close to up/down then tighten down the 2 outer screws. Now you can adjust the smaller set screws, at the end of the laser, to fine tune it to be the same as your open sights. Check that these screws are snugged down good but don't overtighten.
One more thing, put a piece of tape around the laser's barrel over the four small adjustment screws. If you don't, they can fall out while shooting your gun if they should loosen up. I know because mine did and replacements are hard to find.
Overall, this is the least expensive of the laser sights that I have found and I am pleased with it – in spite of the shortcoming just mentioned. Another issue would be that a tactical light can not be mounted with it on, but I don't think I need one. I recommend this item as an inexpensive option.