I brought this because in our offices they leave the windows open and the mosquitoes swarms right in. This electronic zapper has so far killed no mosquitoes, but it has zapped me once (so I know it works!) I've attempted to use it multiple times but because of its bulky nature it's not effective to swing around unless you have open spaces all around you. Also I swear I see the flies go right through the three layered grid without it ever touching the metal.