A trifle, but convenient. My assistants

If you have rooms such as a toilet, a bathroom (shower), a pantry and other rooms with a “blank” door, then very often there is such a “problem” as the light not extinguished there. It is sometimes necessary to find it turned on only after re-opening this room. Naturally, this is energy consumption, and it’s not safe. At my place there were four such doors. I tried to solve this "problem" in different ways.

Electronic ...
I made an anti photo relay, that is, a photo relay on the contrary. When the lighting was turned on, the signal light turned on. This device was located on the door, a photosensor inside the room (through a hole). With the lights turned on indoors, the photo relay was triggered and the LED on the outside was lit.
The device was powered by a battery (well, pull wires there?). No matter how small the energy consumption was, when the battery was depleted, the LED naturally did not work even when the light was on. Which created a number of inconveniences. Yes, and battery consumption took place.

Pilot lamp ...
He placed an understudy lamp above the front door. When the lights were turned on indoors, an understudy lamp lit up above the door. Forgetting to turn off the lights has already become more difficult. But in order for the control lamp to be noticeable, it was necessary to put direct-glow bulbs (ordinary), due to the long heating of the "savings".

And again there was a drawback of this type of alarm, excessive energy consumption due to the "extra" light bulb. Although how to look at it.
Exit from ...
The way out of this "problem" was found unexpectedly. I sorted out some old things and stumbled upon lamps, already ... three.
There was once a fashion to give a fiber optic lamp SV-1, LOMO, USSR.

I think everyone has these "super lights". It was from this “panicle” that I made an understudy.
I found a suitable plastic duct (preferably with an internal diameter of 2-3 cm, the larger the more visible. By the size of the outer diameter of the duct I made a hole in the door. I have glued doors.

I cut the length of the tube in size and filled it with fiber optic hairs.
He inserted a tube into the hole in the door.

From the nozzles of the shower cubicle, fitted a decorative bezel and glued it to the door. Designating and "decorating" them with my future signaling device.

It turned out both cheaply and angrily. This is how it works.

Without any energy consumption and safe. For me, the problem was solved.
And one more thing, if there is a visitor in the toilet, my lamp will also indicate this. You do not have to check it by pulling the door by the handle.
Recommend.