TASER is a brand name. TASER International in AZ has produced the M26 and X26 for law enforcement, and also a civilian model. It's not a firearm, since no primer is involved. I'm most familiar with the X26, which uses an electrical charge to cause gas to project darts into the target. The darts are connected to the "gun" by wires, over which travel electricity from the unit into the target.

The safety of them has been argued all over the world. People have died after being zapped. Did they die from the TASER, or was it just their time due to medical issues, drug overdose, etc. The darts are intended to be shot into muscle, and with a good probe spread, are very effective. Shoot into eyes, genitalia, throat, or head and it's a problem. I've been shot with a TASER multiple times with no ill effects. They are most effective when shot into the back (large muscle groups) and legs (however, smaller target). Less effective on fat, such as a big belly, or with small probe spread. If you are considering it for a spouse, I recommend a handgun it legal in your area and she's willing to carry it. IMO