Who is not understood to stay locked out, forgetting the keys inside, and not knowing how to get back into the apartment? If the door is not locked, as happens when we are inadvertently locked out and the door does not open from the outside, there are several tricks to open it without creating damage.
On Youtube there are several video tutorials that show and explain to users how to solve the problem in a simple, fast and with tools for everyone. Others, reveal the existence of unknown accessories but definitely practical and efficient in cases of emergency like this.
For example, a video that runs on social for some time shows a tool similar to a pincer that can be inserted into the hole of the peephole, after having disassembled it, and that is able to hook the handle and open the door from the inside.
A special pincer and a trick that takes just over a minute. Useful for when there is an emergency, but there is also the other side of the coin: the system, simple and affordable for everyone, can also be used by thieves to enter the houses to be robbed.
If the door is not locked, the bad guys just disassemble the peephole and insert the instrument inside: the pincer hooks the handle and with a simple "click" the thief is able to open the door and enter the house.
Once you have done this, try to reinsert the key and turn it gently: with a little luck, the door will reopen, even if not at the very first attempt. As an alternative to the spray you could also use graphite powder to be distributed, using a blower, both on the key and inside the locked lock.
The situation becomes more serious wheninstead the key , or worse, a part of the key, remains stuck inside the lock : in these situations need a little 'make scassinator the engraving the plate with a pointed tool at the point where the key is inserted and then grasp the key with pliers.
When dealing with locks from complex cylinders , as in the case of an armored door(both double-sided and European-style ) everything is even more complicated!
The question is rather serious and laborious and most of the time, especially if you have left the keys hanging inside and maybe you do not have a copy of them at hand, you need the intervention of the blacksmith.
In all cases, try not to harm , but remember the haste and anxiety will not be of any help: that you decide to try to open it yourself or to turn to a locksmith, always keep calm!