How do I invoke a durable POA?

There's nothing to activate. It's a document that allows you to act as someone's attorney. You have that power as long as they allow you to represent them.

My husband signed a DPOA which became effective immediately. I had to show original to title company when I sold the house but made copies for everything else. It says on the document what you can do but be prepared to give a copy to all of them you deal with. Carefully sign. I signed husbands name by my name adding DPOA. John Doe by Ann Doe DPOA

You'd do yourself a favor by hiring an elder law attorney just so that you don't miss any of the details.

I also live in Texas and have DPOA for my husband. You do not need an attorney or court order because your DPOA gives you the authority to handle you moms affairs. To be on the safe side, when signing documents for your mom, do not sign your name. You will sign Jane Doe (your moms name) by Nancy Doe,Agent (your name). Always specify that you are signing as her agent on her behalf. When I sold my daughters home, I had to sign the documents just like my examples above. Your DPOA document usually lists what sort of things you can do on her behalf, the only time you would be limited is if your mom initialed a certain item that she did not want you to have authority over. Every item that does not have her approval had to be initialed by her (it's sort of like a line item veto). I hope this helps you.

Unless you are penniless, please do not listen to those that think lawyers are useless. I am NOT a lawyer, but I do live in Texas where you reside.
Spend $250-300 for a consult with an Elder Law attorney. Knowledge is power.
If she is still capable, a house can be handled outside of Probate with a Transfer on Death form but if there are other assets all may have to go through Probate Court.
Does she have a Will? If not and she is not of sound mind it is too late for a Will and the distribution of her assets is mandated specifically by State law. There are too many potential loose ends not to get professional advice. I’ve never seen or known an attorney that sells anything but legal advice. Investment advisors sell the other stuff referred earlier.

When I was made DPOA for a married couple friends of mine, it was effective immediately. I thought that was what "durable" meant. We went to their bank the next day where it had been notarized so they could meet me and understand I was the guy doing this for them now. The bank people were so happy that someone was helping them because my friends were very confused about their finances. I was given medical authority for all their needs. Only their credit card company provided any grief because they wanted to see the original POA form and not a copy. Their investment company had their own POA form that we had to fill out to satisfy them. Once it got started, it has been very straight forward. Any money coming in goes right to their bank account. Any money going out is in response to a bill. I was fortunate that there were no children or family members questioning what I was doing. So, getting the POA part going was the easy part. Finding a place suitable for their needs and then going through all their belongings, getting rid of the furniture that didn't come with to their memory care apartment and selling their condo took a while, but it has all worked out very smoothly. The wife had already been diagnosed with frontal temporal dementia and the doctor's were well aware of the husband's failing memory, so proving anything wasn't necessary.

You need legal advice, each state has its own laws. AARP has free legal advice, but I think you have to be a member. If your mom gets social security sign up for being her representative Payee, you don't need a lawyer. Some title companies do not recognize P.O.A. They do accept Guardianships, and Trust's. Are you a Trustee? Can you get a notary to validate your P.O.A? You will need them to go where your mother is because she will have to sign. You can print a copy of a P.O.A. online but you need to revise it for your circumstance to cover everything you need it to (why you need a lawyer) then get it notarized and then it is legal.

Seems like it would be easy to deal with banks and utilities online, so no one ask even asks to see any documentation. The only ones who would be in a position to question your decisions are your siblings or other relatives. Steer clear of estate lawyers and elder law attorneys as much as possible. They are salesmen first and foremost, and they would like to sell you expensive, complicated arrangements that you probably don't even need. The ideal outcome for the attorney is that he/she charges a few thousand for a trust, then charges an extra annual fee for being the "trust protector" or "third-party trustee." Charges a few thousand for the will and POAs, then names himself executor, keeps a retainer, and charges thousands for that service when mom passes. The attorney would really like to be named as an agent or successor agent on the durable financial POA. They'd also like to sell you an annuity and long-term care insurance. Etc. etc. etc. One of the sales tactics of these attorneys: after they play on your fears and you and mom are in a state of panic over impending doom, they plant seeds of suspicion in every family member, so that mom doubts the ability of daughter and son to handle financial decisions responsibly, and siblings suspect each other of mishandling mom's money. Just go do what needs to be done, until you hit an obstacle you can't get past.

My mother’s says when it’s effective. Who made it up? You usually have to show them it, they make a copy and that’s that. Sometimes you get a jerk who refuses to take it. My stepfather ‘s estate is not finished yet so my mother, in the hospital with a broken hip at the time, had to sign a paper ( she is not the executor) but the judge refused to allow my sister to sign for her even after she was told she has dementia and a broken hip, nor would the judge extend the date so we literally had to transfer my mother TO THE Court so she could blather on incoherently and only sign after they literally showed her where to write a scribble. It was ridiculous when my sister had a valid POA!!!!
medical POA for her( my part) is only valid after she is declared incapable of making decisions. If you go to get one, have that made immediately as well. I’ve never been challenged since it’s pretty obvious my mother is confused but something like the above would be a mess. And they still take their word if DNR no matter what the paper work says.

With my mom, I called her lawyer to see about this & after 2 minutes the lawyer said "when I saw her last month I didn't know why she came when she walked out so I'm saying that the POA is activated as of now" - I had to have this confirmed in writing & backed up by her doctors [she was in hospital & there was no problem there] for government issues like her pensions etc. -

I live in Ontario but from what I've seen here generally you need a doctor to deem her incapable of forming decisions for her own welfare & that she needs help with these tasks -

I used a 1/2 size coiled school book with multiple dividers from the dollar store - each section had designated uses such as - medical, financial, important phone numbers etc. - when in doubt document everything - this book was small enough to fit in my purse if I needed to bring it with me & then I could keep my hands free to help mom

My sister was back-up so after every appointment I wrote up a summary in an email with names addresses etc & copied myself so that I could quickly refer to past appointments - if something happened to mom when I was away then she could have been right in the loop - we never needed this but it was 1 less worry to deal with & she could never say that she wasn't kept up to date on mom's health

I hope this helps & I did this from day 1 - FYI until you have everything in order & running smoothly take those POA papers with you everywhere because you'll need them for some of the most unusual items

Did an attorney prepare the POA? Read the document, there are usually instructions on what to do to activate it if it is a springing POA. Or it may be a standing POA.

Check with her attorney.

She is on hospice? The POA will expire upon her death. Has she also assigned an executor?

I am POA for my mother and didn't activate it. In all situations that required my mother's signature, I became the signatory -- her health care, fixing her house, etc. I keep a copy in my car as I live 75 miles away, in case I am doing something on her behalf and a copy is needed. As it comes to her house/possessions, the first thing I did was have the house re-keyed. Since 1965 when my parents bought the house, who knows how many people have copies of the keys (maybe none)? But that way I know I am the only person with keys. As people are helping me get the house ready for sale, I don't tell them my mother's story. I simply call them in, get estimates, and move forward. As long as you have POA, you can proceed. As a fiduciary you need to be prudent about your decisions and keep paperwork on everything you do. But you are the decision-maker.

Assuming that the document was signed and properly notarized, for most matters you merely inform whoever you want to conduct business with on her behalf that you are DPOA, and allow them to retain a copy of the executed document as proof. Unless it stipulates conditions, it was effective when it was executed / signed. Insurance companies and banks will absolutely require a copy before they do, or answer, anything for you.

There are generaly 2 types of poa , durable poa and medical poa both troublesome in some manner, durable poa is most generaly for finances and medical poa is for medical decisions , usually needs to be activated by at least 1 doctor specifing incompatence , once activated it gives you the power to make all medical decisions. Durable poa is for finances most generaly is active as soon as its signed and witnessed, some banks will require that there be a signature form on file and generaly a trust with both names on it ,ie ( John and Jane trust ) In any case it should be set up with a legal expert in Elder Law , they can dot all the i's and cross all the t's, most generally they do a will at same time.

Medical poa in activating requires 1 or 2 doctor signatures stating imcomtency and it goes before a probate judge ,usually quite simple but may be easier to handle with a lawyer, not necessary though

This snippet is specific to Texas:

"If you are entrusting your agent to conduct real estate transactions for you, the power of attorney document has to be filed with the clerk of each county where the property is located."

So, I should head to your county's official website and look for guidance there. They mostly have good search engines, just type in "DPOA" to start with and see what comes up,

You should also take out the actual DPOA documents and have a good read of them. If there's no helpful instructions included, you might do worse than go back to the lawyer who helped draw them up and say "now what?"

You present it (show the originl and they'll make a copy) to her fiancial institutions, her utility companies, her doctors, maybe the pharmacy, Social Security Administration, insurance companies, etc. Once they have this on file you shouldn't have any problem transacting all her business for her. You should keep the original in a safe place. Usually PoAs are General Durable PoAs, so you have pretty much all authority over your mother's property and maybe her healthcare decisions (although often healthcare is put in a separate document). In the eyes of the law, you are your mother when exercising your PoA.

Re when to invoke: if your mother has followed your state's law on PoAs (usually they need to be notarized), once she signs it and gives it to you it's a done deal and you can use is whenever necessary. There are obligations you probably already understand, e.g. to keep her property safe and separate from yours.

Sign Onboard to Whatever it asks But go see a NOTARY for the Witnessing and Signing as well...A Lawyer too can help but Costs money.

I think the POA gives you the ability to do all of these legal things on your moms behalf. Any bank, realtor etc should see you as your mom or an extension of her. That's the way it has worked for us. Now Mom has never objected to anything we were doing but the POA gave us the ability to speak and sign for her, we haven't run into a problem with any one/business.

As a practical matter, it should not take any legal action to use your POA. Your mom’s in hospice and medical folks may ask if you have a POA but usually will take your word and allow you to make decisions if it’s clear mom is no longer competent.

be ready to supply a copy if requested and as others suggest, read it carefully.

I did everything for my folks for years, medical, finances and so on. The only folks that wanted copies of POA were banks and such. And they could be real jerks even with a POA. The docs, hospitals would just ask...ARE YOU POA? Well we’d like to do such and so....

Our POA was effective as soon as it was signed and witnessed but some POA's need to satisfy conditions (generally proof of incompetence) before becoming active, what does your POA document say? Everything you need to know should be on the forms, if you can't understand what they say then ask the lawyer who drew it up.

The first thing that you need to do is read the Durable POA document and see what the requirements are in order to invoke the DPOA.  Also, talk with your Mom's attorney regarding invoking the DPOA. 

Most states require that the person be declared incompetent by 1 or 2 doctors or require a specific event to occur before the DPOA can be invoked unless the DPOA states specifically that "the person does not have to be declared incompetent" or that "the requirements of state statute #_____ does not have to be met in order of DPOA to be invoked" or "This power of attorney is not affected by my subsequent disability or incapacity." [https://hhs.texas.gov/laws-regulations/forms/miscellaneous/sdpoa-statutory-durable-power-attorney]

If the DPOA document states "This power of attorney becomes effective upon my disability or incapacity."; then you will be required to prove that your Mom is disabled or incapacitated.  See the website link that I listed above.