Why do Swedes install small mirrors outside their windows?

We are used to hanging curtains and light curtains on the windows. This is done for various reasons. For example, so that no one looks into the apartment, for comfort and a special atmosphere, and sometimes even for a little insulation (if we are talking about thick curtains, so that there is less wind). But the Swedes have completely different habits... Not only do they not use window decor, but they also attach a small mirror to the window frame on the back side of the window. Why are they doing this and what do they want to achieve?

Why do Swedes need mirrors on the windows facing the street?

It started back in the 17th century, and installing a mirror was a mandatory procedure for every home in Sweden. Now, of course, this tradition is no longer so strict, but the Swedes still continue to hang a small mirror on the back of the window. It is installed where people spend most of their time - either in the living room or in the dining room.

In fact, there are at least three versions of this strange feature.

The first is that Swedes spy on their neighbors and passers-by in this way, discussing them over a meal or just when they are bored. As they say, in Russia the main tool for gossip is a bench at the entrance, and in Sweden this role is played by a mirror.

The second version is that this is how the Swedes monitor their home so that some thief is caught in time and the alarm is raised. In theory, the owner of the home will easily notice an ill-wisher who, for example, went into the garden to steal crops, and will immediately come to the defense of his personal plot.

Well, the last version, and perhaps the most practical and plausible - in a similar way, the residents of Sweden are trying to attract such rare sunlight into their homes, which is so lacking in the Scandinavian countries. In fact, this is also where the habit of doing without curtains comes from - nothing prevents the rays from penetrating into the room. Well, a mirror can reflect the sun and direct it inside the house - for heating, comfort, and just a good mood.

Which version, in your opinion, is the most truthful and adequate? Why do Swedes hang a mirror on the back of the window? Is it curiosity or practicality?