I know there's an actual word for this. I used to know the word, but I've lost it.

The word describes a category of methods that someone uses to detect if someone has been in a room, or opened a door, or drawer, or folder, etc...

Examples: 1) Putting a strip of paper in a door jam, so it falls if someone opens the door. 2) Putting powder on the floor that will be removed or scattered. 3) Putting a ball behind a door in a specific location, so if the door is opened, it can't be placed back where it was with certainty. 4) Putting tape across a drawer that will be broken if the drawer is opened.

I imagine this word would be associated with forensic science, security, or criminal / legal work.

  • Can you remember where you heard it? A James Bond film? A police documentary? Aug 1, 2015 at 21:55
  • Might the single word be an acronym like PIDS (Perimeter Intrusion Detection System)?
    – Avon
    Aug 1, 2015 at 22:10
  • 1
    The Goldilocks Test.
    – tchrist
    Aug 1, 2015 at 23:58
  • I read about it in a non-fiction book about spies (that I can't remember). It was a weird word and seemed really specific to the one purpose. Aug 2, 2015 at 21:00

3 Answers 3


In the British Army, that's just called a 'tell'.

  • Of course, "tell" is also used in, eg, poker, to refer to a player's tic or other action which provides a clue to the cards he holds.
    – Hot Licks
    Aug 2, 2015 at 2:47
  • I think that maybe this was the word, I just don't remember at this point. In any case, it's specific enough for my purposes. Aug 6, 2015 at 17:49

You may be thinking of:


  1. Something that indicates or reveals information; a sign.1

Also from Wordnik

n. A machine or contrivance for indicating or recording something, particularly for keeping a check upon employees (factory hands, watchmen, drivers, etc.) by revealing to their employers what they have done or omitted.2

n. Something that serves to reveal something else3

In this way, the paper you place in the door is a contrivance for indicating or recording / revealing whether a person has entered the room.

And as @SamBurns correctly states, this is often shortened to simply a tell.

1 American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
2 Wiktionary, Creative Commons Attribution/Share-Alike License
3 The GNU version of the Collaborative International Dictionary of English


The "category of methods" you list in your question ("has been in a room" or, opened a door, drawer or folder) all fall under the umbrella term "intrusion". So maybe the term you're looking for is:

Intrusion Detection System

It's a term commonly used in computer networking to describe security applications that patrol for malicious activity (Wikipedia).

Maybe the term has other applications? Home Intrusion Detection System, perhaps?

Also, your example scenarios, when they work as planned, may result in a:


a thing that makes an inadvertent revelation ~ Google definition

dead giveaway

an unmistakable and definitive clue ~ Dictionary.com

something that reveals a fact or an intention completely ~ The Free Dictionary

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