People love to argue with me about this to the point I now have a canned response:
All due respect, in my expert opinion (not joking, take it or leave it), I'd say don't make a warning call, you're probably causing more trouble by making two phone calls instead of one.
Just call the emergency number and tell them you're testing equipment that you have reason to believe may be faulty.
I have made test calls to 911 literally hundreds of times after PBX installs/upgrades. Not a single dispatcher has ever made a negative comment. Not a single dispatcher has even spoken to me in an annoyed tone of voice. I've never heard of a colleague making announcement or warning calls. My training was to make test calls, never to make a "warning" call first.
Again I know you mean well, but what do you expect the police department to do with this warning call? Call the 911 call center, and then what? You think they send out a memo, all the dispatchers read it and say, "hmmm, John Doe is making a test call." Do you think they will compare all calls that hang up to your number? How long will it take to get this information? How long should they ignore your number?
Or, you go the extra mile with 911.gov's puzzling advice and call the police department, get the 10-digit number for the 911 call center, call that 10-digit number to the same 911 call center, just with a different number, then call them again with 911... so you're in essence calling 911 twice instead of once.
The reason I care is that 911.gov suggests a three-step process where the first two steps are, in a practical sense, meaningless... the extra steps will deter people from testing their phones at all, and therefore costs some number of lives.
No. I don't accept it. Just make the emergency call unannounced. Seriously. It will be fine.
Again, I install PBX systems for a living. You can absolutely test 911. Call it and say, "I'm sorry to bother you. I'm testing 911 with new equipment." Completely OK to do. Your call will either work or fail.
Worst case scenario an officer comes to your house (really, really exceedingly unlikely; contrary to popular belief they don't just send cops to a house for disconnected 911 calls without a good reason to believe something is wrong), explain what happened: "I was testing equipment I had reason to believe was faulty, I'm so sorry for the trouble, thank you so much for checking on the call."