Special door lock

Hi John,
Thank you for thoughts.
In mean time I checked this https://securitysnobs.com/Types-Of-Locks.html to understand more.
It is about my parents, over 75.
The person inside, my father, has a key and locked the door, there is a doorbell and even dogs. If my mom comes late then she has a key and opens from outside. But she cannot do it if my father forgets the key inside the door lock. Of course there is the doorbell and also the dogs that bark in case of such unpleasant situation. But there is a case when none of these work. Then it would be good if my mom could open the door from outside no matter if it was locked from inside and the key forgotten in the door lock.
That door is a strong metal door that gives access to a small entry yard and the house with the rooms are in the back. It is not a question of fire hazard.
As I was child, we had a special place to hide the key and we did that for many years, but now that is not practiced anymore, too many thieves and criminals. That is practiced only at some villages, but not anymore in the cities, at least not on the street where my parents live.
I just need a "special" door lock for them.
The code unlock is too sophisticated for them.

The only real option that will meet all your needs is an electronic deadbolt.  You can get them with fingerprint readers or keypads or both.  They're not cheap, but if it prevents what happened from happening again it will be well worth it.

http://www.homedepot.com/p/iTouchless-Bio-Matic-Fingerprint-Silver-Right-Handle-Deadbolt-Door-Lock-BM002U/203052285

http://www.ebay.com/itm/iTouchless-Weather-Proof-Keyless-BioMetric-Fingerprint-Deadbolt-Door-Lock-BM002U-/350795685926

You would want an exterior key override as mechanical fingerprints are definitely not foolproof

Right on John.  They have batteries and start beeping when change required.  But elderly people may not hear it, I understand.

Sounds like what Viki want is close to what's called a Classroom Security lockset, or a commercial use locksets.

Stand alone double deadbolts are not recommended because a lost key can hinder egress in an emergency.

John has the simple, cheap, foolproof solution.
"Why can a regular deadbolt not work? Dad does not need a key to lock; Mom can still get in; both go out you need to lock with a key outside and so cannot be locked out "

OK, I got it, "regular deadbolt".
Could you please suggest me some, eventually with pictures and prices?
I watched next: https://www.youtube.com/watch?v=l-gc1RjxNgk

How about this "safety"?
https://www.youtube.com/watch?v=6GS23gk56H8
https://www.youtube.com/watch?v=jTw1USPGXM4
https://www.youtube.com/watch?v=EtD72PA6FVI


Here is the 2nd restriction for the problem.
The existing door lock is a metal recessed/embedded type with handle similar with the 1st one, top picture from here (mortice lock):
http://www.igloohome.co/blog/smart-lock/the-basics-of-door-locks/
The door is metallic and the space allocated for the door lock has specific dimensions. It is not easy to install another door lock if has a different dimensions. It requires metal work on the door, which I would like to avoid as much as possible. If there is no other chance, then of course we call a specialist to modify the door for the new door lock, but I would prefer to avoid that step.
The door lock has handle to open/close the door and integrated a lock system.
A deadbolt seems to require additional installation work on that metal door.
I do not know now the dimensions of the existing door lock, but I will try to find out.
Actually the door lock is similar with this one and they use “big” keys:
http://mpc.assaabloy.com/yalefile//Fetchfile.aspx?id=11314&ft=.jpg&mh=420&mw=1020
I was thinking that if I use a similar type with similar dimensions but with cylinder as next one:
http://mpc.assaabloy.com/yalefile//Fetchfile.aspx?id=11316&ft=.jpg&mh=420&mw=1020
http://mpc.assaabloy.com/yalefile//Fetchfile.aspx?id=11319&ft=.jpg&mh=420&mw=1020
http://mpc.assaabloy.com/yalefile//Fetchfile.aspx?id=11308&ft=.jpg&mh=420&mw=1020
but the cylinder to have inside as you suggested at deadbolt, no key, but only something to turn and lock. I think that would be the best to be compatible with the existing system/metal door.
Any suggestions or comments in that direction?

I cannot get  a "bonded locksmith" in that area, only a locksmith.

The website https://www.locksonline.co.uk/ is down or I cannot access it.
Could you provide a link with another "double cylinder with anti-lockout"?

A regular locksmith should be good enough. Get one who has been around locally for a while.

Schlage is quite expensive here in Europe.
What do you think if I get some cheap Chinese copies as:
https://www.aliexpress.com/item/Wholesale-Stainless-Steel-Deadbolt-Security-Door-Lock-With-Key-Safe-Lockset-None-Handles-Entrance-Door-locker/32710565837.html?spm=2114.01010208.8.89.IcXJKl

https://www.aliexpress.com/item/Home-Door-Gate-Single-Cylinder-Deadbolt-Chrome-Metal-Dead-Bolt-Door-Lock/32283916169.html?spm=2114.01010208.8.19.0ImNHu

You would need some help with local people. Cheap copies can break or stick (jam) so you would need some local guidance.

Now https://www.locksonline.co.uk/  is online again and I could see the recommendation.

The one on the left looks OK. It is impossible for me to say from a totally different country what might work best for you. A common self-contained deadbolt lock is what you are looking for.

I think the situation is clear.
I will speak with the seller anyway before I buy something. Maybe we can find a local seller/dealer/locksmith to suggest what is available there in the town.
Tira25 had a good suggestion with the external KeyGuard Pro.
Thank you for all comments and suggestions.
It seems, after all, that was not a special door lock, but rather a common type.

Thanks for the update and good luck with getting a good lock.