It hasn't been effective for me. I've put up two bat boxes, and neither has had any tenants in the 8 months they've been out. There are plenty of bats around, maybe they've got better housing options. The ones I observe occasionally fly low to the ground and near the house (it's a thrill to get buzzed by one), but mostly they're further away and higher up and we still get plenty of bugs, including mosquitos in the house. Bats probably do help reduce the numbers, but all it takes is one mosquito to ruin your night.