Canary Trap - Barium Meal Test

Barium Meal Test

According to the book Spycatcher by Peter Wright (published in 1987) the technique is standard practice that has been used by MI5 (and other intelligence agencies) for many years, under the name "Barium meal test". A Barium meal test is more sophisticated than a canary trap because it is flexible and may take many different forms. However, the basic premise is to reveal a secret to a suspected enemy (but nobody else) then monitor whether there is evidence of the fake information being utilised by the other side. For example, the double agent could be offered some tempting "bait" e.g. be told that important information was stored at a dead drop site. The fake dead drop site could then be periodically checked for signs of disturbance. If the site showed signs of being disturbed (in order to copy the microfilm stored there) then this would confirm that the suspected enemy really was an enemy e.g. a double agent.