Crimson Trace revolutionized the weapon laser market. Their innovative pressure switch technology has added useability to an otherwise awkward add on part.
Crimson Trace has been creating grip integrated lasers for over 20 years. The product will usually replace your existing grip panels with a set of rubberized, wood or G10 grips that are equipped with a laser. The activation is the really useful part. Most of Crimson Traces existing units are activated by a pressure switch that is located on the grip frame directly under the trigger guard. What this means is that as soon as you get a solid grip on the gun, the laser is automatically activated. This activation eliminates the need to actively turn on your laser, which would add another step to your draw process.
Another benefit of the grip mounted laser is that it does not change your holster needs. If you add something to the accessory rail under the barrel, a new holder is required. If, however, the laser is added to the grip (that is not covered by the holster), no modification is needed.
These lasers are fully windage and elevation adjustable, offering you point of aim/point of impact matching at a variety of distances. While a laser is never a replacement for your existing sights, it can be a great augment to your handgun.