An old Android phone has a speaker, a clock and a network connection, which is everything a plug-in ultrasonic repellent has and a little more: you can schedule it, change the tone, stop it from anywhere and watch what the phone is doing. AndrIoT exposes that as a tone generator with presets for insects, rodents, dogs and cats, with a level, a duration and three patterns.
The honest part first: published evidence for ultrasonic repellents is weak and mixed, the phone speaker is the weakest link, and results depend on distance, line of sight and how used to the sound the animal becomes. This guide covers what the tone can realistically do, how to set it up and test it, and where a different method will serve you better.
Key takeaways
- The deterrent is a generated tone between roughly 17 kHz and 23 kHz. It is inaudible to most adults.
- A phone speaker usually rolls off sharply above 18 to 20 kHz, so a 23 kHz tone may be quieter than the app asks for. Use the 3 second test to hear what your handset can do.
- Ultrasound travels like light: it is blocked by walls, glass, furniture and curtains. It has to point at the area.
- Constant tones stop working because animals get used to them. Short, irregular bursts work better than all-day playback.
- Do not use it on animals in your own home for hours, and check local rules on ultrasonic devices.
What the phone actually plays
The app writes a sine wave straight to the audio output at 44.1 or 48 kHz, so the highest tone it can produce is about 23 kHz. You choose a start frequency, an optional end frequency for a sweep, a pattern and a level, then a duration between a few seconds and an hour, or no limit at all.
- Patterns — steady is a flat tone, pulse switches on and off about five times a second, sweep slides from the start frequency to the end frequency. Sweeps are harder to ignore than a flat tone.
- Level — output amplitude from 10% to 100%. There is a ceiling, so a later command cannot push the phone speaker past what it was designed for.
- Duration — a run stops by itself, and Stop works from the dashboard at any time.
- Presets — insects and mosquitoes around 17.5 kHz sweeping to 20 kHz, rodents around 20 to 23 kHz, dogs around 18.5 to 20 kHz, cats around 21 to 23 kHz.
The limiting factor is the handset, not the software. Most phone speakers are designed for speech and music and fall away steeply above 18 kHz, and the app says so instead of pretending. That is also why a cheap dedicated device with a piezo horn can be louder at 25 kHz than any phone.
Which animals respond, and how strongly
| Target | Hearing reaches roughly | What to expect |
|---|---|---|
| Insects and mosquitoes | Tens of kHz for many species | Weak and inconsistent. Several studies of repellent apps found little or no effect |
| Rodents (rats, mice) | 50 to 80 kHz | Mixed. Lab results do not reliably carry into a room full of furniture |
| Dogs | Up to about 45 kHz | Often startles a dog at close range, then stops working as it gets used to it |
| Cats | Up to about 64 kHz | Usually ignores it. Cats are the hardest sell of the four |
| Birds, squirrels and larger animals | Varies widely | Not a realistic use for a phone speaker |
Treat all of this as "may discourage", not "will repel". A deterrent that works in one room can do nothing in the next one, and no device like this should be the only thing protecting something valuable.
Setting up a deterrent run
- Open the phone in the dashboard and go to the Audio tab, then the deterrent card.
- Pick the preset that matches what you are dealing with, or choose Custom to set the frequency yourself.
- Choose a pattern. Pulse or sweep for animals, sweep for insects.
- Set the level and how long it should run. Start with a short run, not all day.
- Press Test for a short tone. If nothing changes, the animal may simply not hear it at that distance, and a child or a young person in the room may hear a faint whistle even when an adult does not.
- Press Play tone and watch the badge change from Idle to Playing.
- Move the phone to the spot you actually care about and repeat. Placement decides the result more than any setting.
To make it repeat, add a scheduler rule on the same phone, for example a two minute pulse run every hour in the evening, instead of a single endless playback.
Placement makes or breaks it
- Point the speaker at the area you are protecting, with nothing in between. Glass, a wall, a sofa or a curtain will absorb or block it.
- Keep it close. High frequencies fade quickly with distance, so a phone two metres away is much more useful than the same phone across a room.
- Do not put it in a cupboard, behind a curtain or under a cushion to hide it. That silences it.
- Aim it away from where people sit, especially children, and away from your own ears when you are testing.
- A mesh or dust cover over the speaker cuts the high end. If your phone is in a case, check that the speaker slot is open.
Why it stops working, and what to do instead
Animals adapt. A tone that startles a dog on the first evening is background noise by the third, which is the single most common reason people call these devices useless. Short, irregular bursts are harder to dismiss than a continuous tone, and combining the tone with something the animal cannot learn away, like a light switching on or a sound it does not expect, works better.
For most jobs a different combination does more: motion-triggered alerts so that you know when something is there, a light or a spoken message, a physical barrier where possible, and for insects, removing standing water and using screening. The phone is good at reacting and telling you what happened. See the motion and alerts guide and the scheduler guide.
Animals, neighbours and the law
- Do not use it as punishment on an animal in your own home, and do not leave it running for hours in a room where pets, children or elderly people stay.
- Do not aim it into a neighbour's flat, garden or at their animals. That is a nuisance at best and can breach noise or animal welfare rules.
- Some countries and regions regulate ultrasonic deterrents, and animal welfare law applies to stray and wild animals too.
- Sound pressure drops fast with distance, but at close range it can be genuinely uncomfortable. Keep the phone away from ears and never aim it at someone's head.
If an animal is living in your wall, attic or chimney, deterrents are the wrong tool. Humane exclusion, sealing the entry and, where needed, professional help solve it properly and legally.
Putting it on a schedule
The deterrent is a normal action in the schedulers, so you can run it with the days and times you choose, per phone, and turn the rule off without losing it. A typical setup is a handful of short runs at dusk, when animals are moving and people are not in the room.
If you want to know whether anything is happening at all rather than guessing, point the same phone at the area and let the motion alerts run for a week. The motion and alerts guide explains how to keep the false alarms down.
Pros and limits
Pros
- No extra hardware beyond an old phone that is already running AndrIoT.
- Tone, pattern, level and duration are adjustable, and playback stops by itself.
- Works from anywhere, and can be combined with schedulers and motion alerts.
- The app reports when the handset cannot reproduce a tone well.
Limits
- Phone speakers roll off above about 18 to 20 kHz, and 48 kHz playback caps out near 24 kHz.
- Ultrasound is blocked by walls, glass and furniture, and fades quickly with distance.
- Published evidence for ultrasonic repellents is weak and inconsistent.
- Animals get used to a constant tone, so results fade within days.
FAQ
Can an old phone really repel mosquitoes or rodents?
Do not count on it. The tone is real and some animals react at close range, but published tests of ultrasonic repellents show weak and inconsistent results. Treat it as one small measure, not a solution.
Will I hear it?
Most adults cannot hear above about 17 kHz, so usually no. Children and young people can hear higher, and some people notice a faint whistle or a pressure feeling. Test at a low level first.
Can it hurt my dog or cat?
At close range and high level it can be startling or uncomfortable. Do not run it for long periods where your own pets stay, never aim it at an animal's head, and stop if the animal shows stress.
Why does it not work through a wall?
High frequencies are absorbed and reflected rather than bending around corners, so the sound has to reach the animal directly. Place the phone in the area itself, in line of sight.
How loud should I set it?
Start at the preset level, test for three seconds, then raise it only if you can see a reaction. Louder is not automatically better, and beyond the speaker's limit it just distorts.
Can I schedule it?
Yes. Add a scheduler rule for the phone with the ultrasonic action and pick the days and time. Several short runs work better than one long one.
Is it legal?
It depends where you live, and animal welfare and noise rules still apply. Do not aim it at neighbours or their animals, and check local rules before leaving it running.