Any hotlines for suicidal persons? Are there hotlines for the person with dementia to call?

CALL 9=1-1 IMMEDIATELY WHEN THIS HAPPENS. They will divert the suicidal person to HELP.

Everyone should also know about the The Institute on Aging's 24-hour toll-free Friendship Line, which is the only accredited crisis line in the country for people aged 60 years and older. 1-800-971-0016.
https://www.ioaging.org/services/all-inclusive-health-care/friendship-line

You can also refer a lonely or depressed older adult to them.

Their info page doesn't specifically mention dementia, however that is such a common issue among frail older adults that I imagine their trained volunteers have experience with this as well. Hope this helps!

I'll suggest a digital age option, VRchat. It's like the chat rooms of old except it's a 3D world now. People do all kinds of things. Some people just sit around and watch movies together. Others dance. Mainly people go around and annoy one another by talking to each other. Now this isn't a good option for people that are seriously suicidal, people online can be mean, but based on your post your mom isn't suicidal, she just wants people to talk to. She'll find plenty of that in VRchat.

https://www.vrchat.net/

You state that all she wants is a caring listener. My mother does not have Alzheimer's but her world and circle of family and friends has diminished to the point where I am the only one she wants to talk to about EVERYTHING. Anything that happens, anything that doesn't happen, any reason she can think of, and she is not a person of few words. And overwhelmingly negative. Not to mention stories I have heard more times than I can count. I have often wished there were ways to connect such people as herself to each other, places to call for information, etc. Not emergency resources, just everyday access.

In some cases, persons with dementia qualify for hospice or palliative care. They often send a volunteer to act as a companion. It will give you a break, and the person you are caring for someone else to talk to.

If the person is a Veteran or caring for a Veteran call the local VA or any VA for that matter the prompts will direct you what to do.
The Suicide Hot Line as well, number posted by Segoline.
You can also call the Alzheimer's Association they will help a lot, they have counselors that will answer the phone.
And Call your Primary Doctor. They will refer you to a Therapist and if this is a crisis situation they will get you a very quick appointment. This might be the thing to do in any case as you or your loved one will need a place and person that will help on a long term basis. This is not a sign of weakness, as a matter of fact I think knowing you need help and seeking that help is a sign of great strength,.

An amazing father. A true American hero and a God inspired individual who maintained spiritual focus.
If he can observe a loved one on all the medical assistance devices and conclude that it's worse than what the Japs did to him, what does that tell you?
My wife and I have registered DNR's with local first responders as we both have life ending diseases. Our kids don't agree with our decisions. Try and find peace through Christ is my best advice. The spirit within us is what we are, even though such supernatural knowledge & acceptance is at great odds with our conscious selves. Seek out leaders that recognize you, and share your concerns with them. Together, you will find peace & acceptance just as your father did.
God only knows the inner parts of us, not some Ph,D. making money with their expensive educations.

The National Suicide Prevention Hotline is 1-800-273-8255.
But, it's not a long term solution. You need respite. Is there funding for a home care companion, or respite in your area such as an adult day program? I know you are reaching out for services to help your mother, but you need to help yourself too. Come here to vent and share, I even find some good laughs. But also consider putting a formal plan in place to get yourself some relief before you totally burn out.

Most of these have a chat line too.
I am the adult child of a parent who committed suicide for health reasons. More than 4 decades ago. I was 18.

He was terminally ill. A fact he kept to himself. He had just seen my mom's dad, hospital hooked up to all kinds of tubes and gizmos. He wanted my mom to promise she did not do him. She could not make that promise.
This was pre advanced directives.

My dad was a POW in Japan for 3.5 years, one of longest held. He was in Bataan death march.

Those of you who might be judgmental about this, I think God cares more about how you lived your life, than how you might have ended it.

Contact the senior center in your area. They often have a program where a caring person will call a senior daily.

In Hawaii, check :
http://www.suicidehotlines.com/hawaii.html

Yes there are. 1. 800. 273.8255.

That is natl suicide prevention hotline. We are going to see this more frequently.