Ok people, thought I had 1 rat. 1st time user of one of these.. Placed in roof an arms length away from manhole. Conveniently, copper pipe across the beams, great for a wrap of the cord, keeping it off the ground, neatly down the manhole edge, place the cover back on & turns out I had 4 rats! OMG. Subtle beeps let you know. Check it as big fella must have approached it cautiously when his 2 young were not there. false/positive. 5 attempts, 4 rats within 24hours. JOY! . All is silent. Don't wait