Eggcorn Forum

The main substitution of “detective” for “detector” makes sense on a few intuitive and semantical levels: both the lie detector and detective are associated with discerning fact from fiction during interrogations of suspects, so in a sense the lie detector acts as an instrument in the domain of the detective thus is an extension of the idea of the detective (a person who finds the truth in a criminal case) itself. Also, the lie detector could act as a detective by analogy, although instead of investigating the scene of a crime for hidden clues, the lie detector probes the mind of a suspect for hidden truths.

A few examples found from searching Google (phrase in bold):

Example 1: Anything Hollywood

Hector said he would take a lie detective test to prove he’s telling the truth. Do you think it’s even necessary?

Example 2: Fan Fiction

Hand – How are you, really? They will make us take a lie detective test!

Example 3: Asia Finest Discussion Board

Thai girls should not wasting their time taking lie detective test. Because the world know that they’re liar already.

Example 4: Yahoo Answers

I live in Illinois and I need to take a lie detective test for little or nothing.?

For “lie detective test” vs. “lie detector test”, I found 17,200 results for “lie detective test” and 2,750,000 results for “lie detector test”. “Lie detective” vs. “lie detector” had results which seemed invalid owing to the fact that there is a person who calls himself the lie detective.

Most of the sites with the eggcorn fit into three categories: normal people asking how to beat the “lie detective test”, normal people asking how to take the test quickly and/or easily (most likely to provide evidence of innocence in some matter, criminal or otherwise), and discussions of celebrities, a subset of which is popular criminal cases in which the participants themselves have become minor celebrities.

Based on the above, my guess would be that the “lie detective test” eggcorn may incidentally result from pop cultural osmosis by way of true crime and celebrity crime stories in print and television media (more specifically, from the accidental conflation of the terms ”[lie] detector” and “detective” through their repeated association within the media in the United States).

Possibly contra that hypothesis are examples 2 and 3, of which 2 has nothing to do with true crime (although example 2 is very much related to US pop culture) and 3 has nothing to do with the United States, pop culture, or crime (although that particular instance of the eggcorn may have resulted from a non-native speaker’s unfamiliarity with the English language, as opposed to the other examples which seem to be from native English speakers).