A molecule which mimics ethyl alcohol when blown into the Intoxilyzer sample chamber. With the 8000C ethyl ether or diethyl ether. With the 5000C limonene or d-limonene. Acetone and Acetaldehyde are possible interferents but may be flagged by the Intoxylizer as Interferent Detect (or subtract on the 5000C). An interferent can create a false positive or aggravate the readings. An interferent can also compromise the reliability of control tests. An interferent may be in the subject's body or in the breath room air.

From a defence perspective, you may be able to use a chemical interferent defence, post Bill C-46 to challenge a "conclusive proof" presumption under s. 320.31(1)(a) arguing:
1. the chemical interferent changed zero for purposes of the air blank, system blank test. rendering a 000 system blank test unreliable
2. the chemical interferent changed the result of the cal. check, system calibration check, artificially raising or lowering cal. check results so that the displayed or printed results of the cal. check are unreliable
(Please note that ambient alcohol in the breath room, can act in the same way as an interferent to interfere with the setting of zero, thus affecting the reliability of the system blank check and/or the system calibration check. See videos, dictionary entries, and blog entries having to do with interferents, air blanks, setting zero, and unreliable cal. checks.)