Let me save you a little time. If you think the trigger is broken on your Sig Mosquito because it wont pull far enough to release the hammer, try putting a magazine in the gun (an empty magazine, in fact get all ammo out of the room when working on a firearm, and check the chamber again just create good habits). The gun has a magazine safety that blocks the trigger bar. Had I read the manual like a normal person I would probably already know this.
I picked up a used Mosquito Sport for my kid. The first thing I do when I get a firearm is strip it down and take a look at the internals. This handgun is kind of a let down as much of the workings are not visible without really stripping it down. I didn’t want to go that far so I put it back together and ran a simple function check. The hammer wouldn’t drop. The trigger seemed to stop as if something was stuck in there. So I stripped it back down again, removed the mag release to see if something in there had shifted, removed the decocker and got a flashlight to see the sear through the tiny opening. After poking at it for half an hour I noticed there were two spring loaded gizmos in the mag-well. One operates the slide lock on an empty mag, the other is the magazine safety which prevents firing the handgun when the magazine is removed. It seems like such a stupid “Feature” to add to a handgun, but ill give a little slack because 22’s are commonly used by beginners with varying levels of safety sense. Some who didn’t have the benefit of a father yelling at them like a drill sergeant. So there you have it, stumped by a feature that is probably listed in the manual, had I the time and inclination to read it.