The Ultrasonic Pest Repeller, Tested by Arithmetic: A Disproof of the Whole-Room Claim

Plug-in ultrasonic devices are sold with the claim that they clear rodents or insects from a room, and often from a whole house. This paper tests that claim with arithmetic alone. A representative stated device output of 100 dB sound pressure level at 1 m at 40 kHz, a more generous stated case of 110 dB at 1 m, a lower-frequency case at 25 kHz, and a weaker case at 95 dB at 1 m are propagated across a room using geometric spreading, stated atmospheric absorption coefficients of 1.4 dB per metre at 40 kHz and 0.6 dB per metre at 25 kHz, a stated 15 dB loss behind furniture, and a stated 25 dB loss through an interior wall. Against a generous effect criterion of 80 dB at the animal — the lowest level at which any behavioural effect has ever been claimed — the representative 40 kHz device reaches that level only out to 5.12 m in a clear line of sight and only 1.6 m behind furniture. In a 5 m by 4 m room, a simple shadowing model leaves only 27.5 percent of the floor area at or above the effect level for the representative device, and only 51.1 percent even for the generous device. Through a wall, the level 3 m away is 62.7 dB for the representative device and 72.7 dB for the generous one, both below the criterion, so an adjoining room receives no treatment worth the name. Meanwhile the level 2 m from the generous device, where a person or a pet may sit, is 102.6 dB — well above the level at which the sound is plainly audible and potentially aversive to dogs and cats. The whole-room and whole-house claims do not survive the arithmetic. SIMULATED, NOT MEASURED.