There's been a lot of talk lately about technology that can prevent someone other than the owner from using a firearm. Unfortunately, the technology is far from mature, with only a single handgun model being sold in a single gun store in the nation. I'm going to go over it, first.
The Armatix iP1 handgun is the first consumer model I know of, and the only one currently available in the USA with some form of owner-recognition technology. It relies on a combination of a PIN code and an active RFID watch to trigger a manual blocking mechanism for the firing pin. If the code doesn't transmit properly, or if the weapon is out of range of the watch, it cannot fire. I see a number of problems with it.
First is the caliber. .22LR is generally considered a target round, and is generally useless in any confrontation due to the precise shots needed to stop an attacker. Full disclosure, I know someone who died from being shot with a .22LR in a range accident, so I'm not claiming this round isn't hazardous. However, in a high pressure, close quarters situation, the accuracy required to use it effectively is very close to impossible. It simply lacks stopping power. Now, I know they will certainly come out with larger caliber weapons with more punch, so this is a temporary problem.
Next up is the alert system, a red/green LED stripe that indicated when the weapon is armed or not. In darkness, this is a massive giveaway of the wielder's presence and position. Again, though, this is a stylistic complaint, largely, though developing a system that both alerts the wielder it is properly armed without indicating it so openly could prove difficult.
Third is the battery. The default position of the locking mechanism is locked. Armatix advertises the watch for 1 year of standby or 5000 rounds on a battery charge, but includes no such description of the battery life of the firearm. Size restrains battery capacity, and failure to charge a firearm would render it quite useless if needed. As they aren't bragging on the firearm's battery's capacity and endurance, I'm forced to assume it's rather poor.
Fourth, you're adding several extra mechanisms to the firing sequence. A short range radio, an electronic reading mechanism, a servo, and a solenoid. More places to have something go wrong, and not as easy for the owner to strip, clean and service.
Fifth is the RFID chip itself. It uses an active chip, which is slightly longer range but more battery intensive, and more subject to radio jamming. Criminals always adapt to what they face off against, and it won't take long for them to start using homemade jammers to disarm their victims. The longer range also makes it more susceptible to readers that mimic its signal.
Sixth, the weapon and watch are a whopping $1800. By comparison, a Springfield XD ranges from 9mm-.45 caliber, costs $400-$600, has triple redundant safeties and two load indicators, and is a quality firearm. Full disclose, I own a 9mm and .45 ACP version of the Springfield, which is why I use it for comparison.
The last problem I see is the situation where someone else must use it. For example, if you have a husband and wife, the husband is wearing the watch, he leaves the home and someone breaks in, the wife now can't use the weapon to protect herself. Doubly so because there's a bright red stripe saying, "Hey! She can't actually use me!"
All in all, we have a target practice pistol for the range that is underpowered for any other purpose, and has several "features" that would prove dangerous to the owner in a self defense situation. It's also priced out of the range of what anyone should expect to pay for a target pistol.
Now, the question is, how do you deal with it?
KISS stands for, "Keep It Simple, Stupid." Classic trigger locks are reliable, functional, and cheap. They've worked very well when utilized properly. Unfortunately, the bad habit some people have of leaving the keys with the weapon will likely be repeated with a rather dorky watch, so it's unlikely to be more effective than a standard locking mechanism.
If a digital device is still desired, it needs to provide silent, invisible alerts when it activates. Two short and silent vibrations, a small heat spot, or the like. It needs to pair with a smaller item, like a ring. A heavier weapon should be able to accommodate a battery to work with a passive RFID chip. The "keys" should be codeable with a short RSA key, whose pair is loaded into the weapon. This would allow for easy cloning of the keys, if multiple people need access, as well as being less conspicuous. The contact-range unlocking should also help reduce the effectiveness of jamming strategies. However, the final points should deal with any Murphy's Law situations: if the gun drops to very low battery (5% or so), the electronic safety should disengage and permit manual operation through a standard mechanical safety switch. If the receiver is saturated with "bad" radio (gibberish, static, or the like) it should do exactly the same until it's capable of reading a key again.
Ideas presented above as solutions are mine, and I reserve all rights to them.