Sounds that are inaudible to humans could be making people ill, according to research.
The increased use of devices like tannoys, automatic doors and even electric gizmos that scare off cats could cause adverse reactions in humans.
It means places like schools, railway stations, swimming pools and museums could be making you ill with "ultrasonic sickness," which can induce nausea, dizziness, tiredness, stomach pain and headaches.
The symptoms are triggered by an adverse reaction to sounds of a frequency of around 20kilohertz - out of the hearing range of most people.
Writing in the Royal Society journal Proceedings A, Southampton University physicist Tim Leighton said: "There has been a massive increase in deployment of devices that operate by placing ultrasonic fields in residential, recreational, and occupational places. Discomfort is likely to be seen in the population as a result."
About one in 20 people can hear ultrasound.
