Monitor is an alternative trade name for the insecticide methamidophos, a systemic organophosphate used against a wide range of chewing and sucking insects and spider mites on fruits, vegetables, and cereals. It acts by inhibiting cholinesterase in the nervous systems of target pests. The active ingredient is classified as extremely hazardous and is acutely toxic to humans, so most countries have banned or severely restricted it. Where any use persists, maximum residue limits and pre-harvest intervals apply, and monitoring programs screen produce for methamidophos residues. Its trade name should not be confused with the verb, and old product labels still surface in developing regions.