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The Gap Under the Infrared Beams (illustration)
FILE No.197Unsolved

The Gap Under the Infrared Beams

Difficulty ★★☆about 5 minTheft CaseSensorsTraces
Someone passed at a height just above the floor. There is a single trail in the dust on the floor.

Case Record

An art museum's exhibition room has infrared sensors. The infrared beams run at fine intervals from 60 cm to 2 meters above the floor. The beams were never interrupted.

Even so, a painting vanished from the exhibition room. In the dust on the floor was a single trail about 50 cm wide.

Your question

How did the culprit get through the exhibition room?

Case Files

Diagram

The gallery, side viewBeams at 60 cm to 2 m above the floorThe beams were never broken. The floor dust shows a 50 cm-wide strip.
Diagram

Hints

If you get stuck, open the hints one at a time, in order.

Open hint 1

At what height above the floor are the beams?

Open hint 2

What does the trail in the dust show?

Open hint 3

Were the beams interrupted?

Solve It

Your question

How did the culprit get through the exhibition room?

Choose the answer closest to the truth.

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The Truth

Crawled along the floor and passed under the infrared beams

The answer is "Crawled along the floor and passed under the infrared beams."

The infrared beams are set 60 cm or more above the floor, so staying close to the floor does not interrupt them. The single trail in the dust matches the width of someone crawling through.

The beams were never interrupted. If they had been turned off, a record of that would remain. Nothing is stated about the ceiling or walls.

Crawling beneath the beamsClose to the floor (below 60 cm)The dust strip matches the width of someone crawling.
Diagram of the solution

Key Points

  • Check the range of the sensors
  • Focus on the traces on the floor
  • What not being interrupted means

Why people get fooled

Because you think the sensors guard the whole space.

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