No arguments here, just as an avid hiker used to bear and cougar country, the best defense is awareness. If you holster a gun and get complacent, well, that’s no solution.
I don’t think you can find a modern Derringer (I use the term loosely to describe any pocket-sized handgun) that lacks a trigger guard. As for the other criteria, as has been noted elsewhere, hitting a mountain lion/cougar that is closing in on you is a tall order with just about any firearm, much less something you’d fit into your pocket. With a barrel that’s perhaps two inches long or less, it’s going to make a mighty loud bang (ok, maybe a loud crack), which seems to fit the OP’s requirement of being intimidating. And if that mighty crack isn’t enough to do the job of scaring away the threat, you’re probably fucked anyway.
Besides, considering the inherent inaccuracy of such a firearm, significant practice/range time is probably not terribly important other than to know which end is the business end. In terms of accuracy, you might be just as well off throwing rocks!
Only @enipla knows what fits his criteria, I’m just spitballing here, but since I didn’t see anybody else suggesting a truly pocket-sized mighty mite, I thought I’d offer it, if only for it to get shot down (heh).
Mountain lions do not normally prey on humans. I have seen the warning signs in California, and I did see one in a park once. It was just sitting there chilling out, and I stayed away from it. Anyway, in the extremely rare scenario a cougar did decide to stalk you, you would not see it coming or have a chance to shoot it before it jumped you.
I have always thought the best defense was to hike with at least one person you can outrun. Sort of like playing poker: if you look around and can’t see the mark, it’s you!
NAA (North American Arms) currently has a couple.
A young man was killed in El Dorado county in 2024. For the most part lions that attack people are starving.
Ah, I see the misunderstanding. When I see derringer, I think the traditional one or two shot, or more rarely mini-cylinder .22 like this NAA pistol mentioned by @thelurkinghorror :
Which is indeed a modern derringer in .22 Win Mag.
And most derringers I see in gun stores are indeed older models rather than more modern ones, many of which (but not all, see this stupid thing!) come in smaller calibers with a trigger guard. So both sorts exist, and I shouldn’t have made as sweeping a statement.
But most of things you talk about are what I see more as pocket pistols, rather than derringers. Different terminologies lead to different assumptions!
Those are best as back up guns, Very inaccurate and usually only two shots.
The only time where it is likely you could shoot or otherwise stop a mtn lion from attacking is after they pounce, say on a pet. But generally humans are pretty damn safe around them.
Good point.
But the trigger, IIRC is partially hidden until cocked. But you are supposed to carry the gun in the safety notch between two rounds on the cylinder.
22 magnum is twice as powerful than .22LR, way more than .25 and about even with the .380.
Has she gone with you?
Oh yes. Both of us at the counter. My wife introduced me as a her husband that knows gus. I say “It’s her gun but I will advise”.
.38spl revolver looks best for her.
It’s simple. Packs some punch. A snub nose is not accurate at all. But an easy carry. Have had three table top lessons so far. Time to get real.
Excellent choice.
Here’s some info on defense rounds. For training I would use cheap FMJ, of course.
That’s what I and 3 gun store guys think as well. The last thing you want when learning/teaching is to over complicate things.
You need to know the basics.
But I will probably buy a .380 so she can learn to shoot it, after she is comfortable with a .38spl. Just so she knows the difference.
We did more table top training with our electronic ear muffs on yesterday. Those need to feel natural, don’t want things to break your focus.
And she does want professional training. She says she found a group that is for women only. I think that’s a fine choice. I’ve trained a lot of people, but not with handguns.
From a product design complaint to an excellent discussion of a way to introduce someone to firearms training and use. Got to love the SDMB.
I could adapt to the new safety, trigger.
I’d go to the range and practice for a few weeks. Develop a feel for the trigger pull and build muscle-memory.
The biggest concern is not having a brain fart if an emergency happens.
You have seconds to evaluate the danger and react appropriately. That usually means doing nothing.
The cat knocked something off the shelf.
I wouldn’t shoot the cat. 
Oh I could too. I’ll always feel that it’s just stupid though.
That looks like it would break your hand.
Oh good lord. Do they sell single bullets? You won’t want another. But what’s weird is that powder won’t all get to burn before that bullet is out the barrel (Well I doubt it)
I’m familiar with the Glock 17 from training as an army reservist. As people have mentioned, the double trigger is there to prevent incidental contacts or drops from pulling the trigger. Part of the field strip and assemble is to test that it won’t fire if a finger either side pulls at the main trigger without gathering in the latch trigger. I’ve never seen this fail. Because the weapons are relatively recent the main trigger simply won’t move.
In terms of safety I think that it is a well functioning system. When on the range I have confidence that the system will work to prevent accidental discharges (as distinguished from negligent safety practices.) An external intrusion like a branch will only fire it if the blade of the trigger is pulled back all together - the latch doesn’t protrude at the base of trigger and a sideways pressure on the trigger is unlikely to translate backward motion unless it pulls back the latch as well. Basically only a motion strongly resembling an ordinary trigger pull will get past the system.
When firing the latch part of the trigger is barely noticeable. You just gather in and fire at a pressure similar to a rifle or a cocked double action. The nice thing about it is when you are firing you’ll never encounter a heavy double-action trigger pull like on the old Sig Sauer P226. New soldiers have more trouble with not working the slide firmly enough, or especially with removing the slide when field stripping. The hold back is also annoying to engage as a lefty, which is perhaps annoying specifically to us since we do a lot of dry drills with notional rounds.
I’m not looking to make recommendations or comparative judgements but I thought my experience might be a helpful guide. Apologies if this has already been covered in the lengthy correspondence!
Thanks @Jaguars . I’m not going to state my opinion on them again.
I took my wife to an indoor range for the first time today. She did great. Seriously. .38spl. First time shooter. and she hit the target about 75% of the time. She was very safe. But I drilled that into her at table top lessons.
I think it helps that she has seen gun salesmen and range officers now, make sure the handgun is unloaded. Always, they check, and check again when putting it back.
And she knows to always treat it as loaded. While a handgun is a tool, it’s a deadly one.
Did another table top lesson with her tonight with my Colt 1911 (after dinner and two games of darts). That gun is way too much for her, But I wanted to show her how to check if a semi-auto is loaded. That’s 4 lessons from me and an hour of range time. She was very safe.
I have Health, Dental, Vision and Auto insurance along these lines. Worked so far, but Gravity is A Bitch!
Most Derringers are very unpleasant to shoot. Especially those in the higher calibers.
And then there’s this little bastard:
