This laser ONLY fits the H&K USP full-size pistol.  If you have any other H&K pistol with a rail that has cross-notches under the barrel, the GTO-G laser also has grip activation:

ArmaLaser GTO-G laser with grip-activation

• 5 Year Manufacturer Warranty!
• Immediate activation - no button to reach
• Laser activates by normal pistol gripping
• Custom fit for your pistol model
• Switch between steady & pulsing beams
• Adjustable windage & elevation (up/down & left/right)
• Master On/Off switch
• Rock solid mount
• (1) CR1/3N Battery: Up to 2.3 hours on time
• Battery door for easy battery replacement
• Bright 520nm green laser beam (more visible in daylight than red)
• Dot Visibility: 1/2" at 50 feet
• Easy installation
• Arma Laser buy back program
• Excellent customer care
• American innovation
• American quality
• Weight: .75oz
• Also available in Red for $118.75

More Info:

ArmaLaser manufactures the most advanced laser systems in the world.  We concentrate one one thing: Turning a laser on as soon as you grasp your pistol. And giving you full control over burn time.  You want it off? Move your middle finger forward a bit.  Then move it back to burn laser again.  ArmaLaser manufactures 5mW 520nm Class 3R Green lasers (green lasers are more visible in daylight than red). The TR-Series's brilliance, however, is on how the laser turns on.  And this is where the TR-Series changes the direction of the firearm accessory.  Only the ArmaLaser switching system has basically no thickness to it.  And you turn it on without needing to do anything but grip your pistol.  There is no bump under your middle finger to throw off fingers onto different levels. And no button to reach in a stressful, possibly disorienting situation.  We feel a linear switch which runs for a certain length under the trigger guard is a better type of switch for the many different types of hands & grips that people have.  The material we use in all our models is DuPont's Zytel ST8018 glass-reinforced polymer which is what most pistol manufacturers use in the their grips/frames.  So our lasers match up in the same material, finish, and color as the pistol.

That's why many people comment that our lasers look like a factory option. You can choose between pulsing or steady beams. Dot is fully adjustable for windage & elevation. A battery door means easier battery changes without laser disassembly. A master switch in recessed into the housing to allow practice without the laser turning on.  Weighs only .75 ounce. Up to 2.3 hours of burn time from for a single CR1/3N lithium battery. Another advantage of touch activation over mechanical switches is that it's not easy to turn on in a holster if something pushes against it.  Rock solid mount, we do mounting as good as it gets.  Easy, do-it-yourself installation.  No gunsmithing, anyone can do it.  AMERICAN INNOVATION. AMERICAN QUALITY: 5 year warranty. Buy back program. Excellent Customer Care.  HIGHEST QUALITY BEST DESIGNED LASER MADE TODAY. Your laser needs to be there for you, without you having to be there for it.