Is there a safe way for someone to keep a gun in their house when they experience suicidal ideation?

No. Yes.

Anything else is overthinking.

This. Pepper spray is a better weapon for defense than guns or knives in most situations where a normal person would need to defend themselves. Easier to use, harder to mess up, and while it's possible to fight through a gun shot pepper spray forces your eyes closed and messes up your breathing, making it very difficult to do anything at all.
- For the humble consideration of the group: pepper spray is really effective at what it does and taking away someone's vision is one of the greatest advantages you can take in a fight. I also agree that guns aren't the exodia for a fight that one might believe. I put stock into knives as a deterrent, but not as much as declaring you have pepper spray and brandishing it.
  
  With that being said, in terms of being a deterrent, I also think a flashlight/tazer combo is a potent deterrent, perhaps superior to pepper spray. In that pepper spray let's someone fuck around and find out because it can look unassuming, if you get a light shined in your eyes and then hear the loud sound of a tazer, I have to believe that you lose the will to fight far faster. The light takes away their vision while giving you more which is super overpowered.
  
  A YouTuber who was an ex cop, martial arts instructor with experience and training in use-of-force has spoken multiple times that "just run" isn't the golden ticket that I once thought it was and I find it persuasive. Even if there is no win condition in fighting besides getting home safely, protecting others, injuries, if they're faster than you, etc. would be part of the calculus too. Which really sucks and is depressing. Not everyone can have a decade of competitive combat sport experience. Things like walking in a group, having awareness of your surroundings, looking tough also make you look like you're not the easiest target in the room which is probably what a random aggressor is looking for.

There is not; correct

I would say no and if you do have a gun in your home and are experiencing suicidal ideation, seek out someone you trust to take the gun from you. If you don't know anyone else who can legally own a gun, give them all the functional parts and keep the receiver.

I've held guns for friends like this,and I know people who keep their gun in a friend's safe and have their friend bring it along only when they go to the range together.

If you already have the gun, I think it would be best to have a friend or family member store it for you until you're feeling better

In Canada, gun laws require firearms to be stored unloaded, in a locked container, with a trigger lock, and that ammo be stored separately. All of the above are measures to delay the use of a firearm, which reduces the chances of it being discharged accidentally or in a moment of intense emotion. If you feel you need to be armed when leaving the house, but can live without it when at home, then taking the above steps will make it less likely that you'll use it on yourself.

Without getting into the debate about gun safety, you are more likely to kill yourself with a gun if you have access to a gun, and if you want to get rid of the possibility, then you need to get rid of the gun. Gun ranges often have storage lockers for guns, iirc, so you could leave your gun at a range for a while if you didn't want to get rid of it. Your safest move is to get rid of it.

I'm really sorry to hear that you're experiencing suicidal ideation. I hope that you have some pathway to addressing the underlying issues causing them. It would be worth seeking out whatever resources are available, as well as let your friends and loved ones in on the fact that you haven't been doing well. However, be careful about talking openly about suicide with people you don't explicitly trust to not freak out. Well-meaning people can end up calling emergency, which never helps because it just means the cops get involved, and you get put on a watchlist, or taken to a hospital, etc. Talking about being depressed, lonely, or stressed is usually safe, and can be cathartic if you talk to the right people.

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NO! No matter what safeguards you implement there will always be workarounds.

I haven't done this for guns but put the key for the lock in a big block of ice so you have to wait until it thaws to get it. Alternatively you can dissemble the gun so you have to lookup the manual to make it ready for use. This just delays use by 15-30 minutes at best though so ymmv.

Practically speaking, pepper spray is the most effective self-defense outside of a gun. Maybe get a pepper ball gun if you need the extra range and you could also threaten someone attacking you into thinking it's a real gun?

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Guardian angel/Kimber pepperblaster (depends on your country) is a hell of a pepper gel delivery device. It's tiny, potent, and pocketable. For home there's plenty of reason to have a nice big plumbing wrench or other blunt heavy object within reach.

That said, not that I would recommend it, I was in that boat for a long time, and made it through. But that's tainted heavily by survivorship bias. I was lucky, there were only a few days where the thoughts went from their normal constant background hum to a real foreground "oh shit" level; in those moments first thing I did was lock away ammo, cable lock the pistol, everything went in the safe, keys for safe ammo and cable lock all went in different locations. Then call someone to talk the feelings through.

Are you actively working on your mental health? Any therapy/meds/counseling?

I'm sorry you have to go through this comrade meow-hug

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As someone who has been super suicidal forever, no! I'm literally shocked and happy that I'm here in my mid 40s. I hope you can be too.

There are ways to make it safer, but ultimately it’s hard to argue for a solid yes, and I reckon there’s studies showing that death by suicide is more likely among folks or households with access to firearms (I know that states with looser gun regulation experience more deaths by suicide overall)

In suicide prevention, there is what’s called “Counselling on Access to Lethal Means (CALM)” where someone might walk you through of ways of building distance (e.g., temporal, physical, etc.) between you and access to a firearm, for example. It would include things like storing ammo or your gun offsite, limiting your personal access to your gun stuff (e.g., store it in a safe that only someone you trust has the code to, not even yourself), keeping your ammo frozen inside a block of ice, etc. Data shows that suicide-related thoughts can fluctuate dramatically in just a few minutes or hours, meaning that many suicidal crises can come and go naturally (for lack of a better word). Anything that will make your gun harder or slower to access will keep you safer for times you experience an emotional/suicidal crisis, but this might contradict why you want your gun in the first place.

It’s also possible that if the police know you have a firearm and they come to you on a “wellness check”, you might be at increased odds of a bad outcome, like police escalating to violence and/or being forcefully detained and brought to a hospital.

I can share some resources or links if you’d like?

Keylock gunsafe, physically relinquish the key to a trusted individual. You can fine tune details to suit your needs, the idea is to make the gun completely inaccessible while you are alone.

Sorry you are having a hard time, friend 😔