What if I live alone and cannot unlock the door during an emergency? What can I do to enable 911 responders to enter my residence without tearing down the door?
Call your local police department and inquire about a "Knox Box Key". They probably have a master already to open one. You will need to buy the one they suggest or have a locksmith get involved to match their key to the box you purchase. They might even have a system set up for your community that you don't know about.
The least expensive solution here is to buy a combo lock key box. You place a key to your home inside, put the box somewhere accessible outside and, if you call 911, you simply provide them the location and code. Just be sure to reset the code between uses.
Alternatively you could buy a door lock with a keypad (example) but this route is far more expensive.
One option is to buy a 'smart lock' that gives you the ability to unlock the door from device such as smart phone or tablet. If you carry a smartphone around, this might be a viable option.
I feel obligated to note, however, that products in the 'internet of things' (IOT) space have notoriously poor software security practices. For example, a lot of internet enabled security cameras have well-known and unchangeable passwords. You would hope that a lock would be secured against simple hacks. Caveat emptor: look into whether anyone has done any evaluation of the security of such products.
This kind of thing comes up often in regards to security (well in my IT security experience at least). You want to make something easy to
break into access for the good folks, without making it easy for the bad folks. This is hard!
Some of the other answers suggested lock boxes with a master key or number combo.
These are not very good.
In an emergency do you want someone mucking about, trying to get the right key or number combo?
Or if it is a well known key, well then sooner or later some bad person will work that out and take advantage of it.
No harm checking with local good folks if they have a well established way of dealing with lock numbers. And if they would use it for their grand mother house.
That way you can see if they trust in that system!, and if it is worth doing!
However what I think you should do is:
Replace the door strike plate screws with short ones (say 10mm, 1/3inch ish) Cheap and simple! However do keep the chain lock screws long and strong!
That way if good folks need to break in, well you will get minimal damage.
But what about the bad folks wanting to kick down the door you say!
Well an opportunist can't tell the screws are short, and bad folks who are going to kick down your door were going to do that (or the window) anyway.
So may as well make it easy for them, less damage to repair! To protect against them you would need to live in a house that resembled a prison cell. Bad Feng Shui, is all I can say.
Get a lock with a built-in electronic keypad.
Then if you ever have to call for an ambulance but can't get to the door, simply tell the dispatcher the code before the ambulance arrives. They will be able to relay it to the emergency responders, who will have no trouble opening the door.
Locks like this typically have keycodes that are 4–6 digits long and are quite easy to operate, unlike the lockboxes that hold a spare key. And once the emergency is over, you can easily change the code.
Here's an example:
Depending on where you live, Smart911 can be a nice option. It is a free system where you can add medical information, access codes, pictures of your children, vehicle information, and other pertinent details that can save valuable time for first responders in emergency situations. (If the 911 answering service is set up with Smart911, they can relay this information to the first responders.) See: https://smart911.com/
Even if your area doesn't have this system set up, it can still be helpful in the event that you are traveling and have an emergency in an area where it is supported. (i.e. If my child goes missing, they can immediately see a picture on their screen when I call for help.)
In my rural fire department you either give a key to the fire chief, who tags it and locks it inside the keybox of a response vehicle, or you give the alarm company (if you have one) or the chief the location or code (or both) for your spare key, or the contact info for your choice of a local "keyholder". Of course, almost nobody here locks their doors anyway, rendering it a moot point in the majority of cases. Obviously, if you're conscious when calling 911, you can also give instructions on which unlocked door to use or where the key is for the locks. Also, each engine has one or more sets of tools for making a forcible (but fairly graceful) entry when justified by the perceived risk of unnecessary delay.
All the answers about lock boxes and such look great. But if you don't have some kind of medical condition where you expect it's likely you'll have an emergency at some point, and if you live in the US, I wouldn't worry about it. As far as I'm aware typically the fire department responds to all medical calls, and they will get in. You'll have to pay for door repairs, but you'll be alive to do it.