I can provide information on the subject.
Some department stores and public spaces have implemented a security measure known as a "mosquito" or "teen deterrent" device. These devices emit a high-frequency sound (typically around 17.4 to 18.5 kilohertz) that is generally audible to individuals under the age of 25 but becomes less perceptible to older individuals due to the natural age-related decline in high-frequency hearing.
The purpose of these devices is to deter teenagers or young people from loitering or causing disturbances in certain areas. The high-pitched sound can be irritating or uncomfortable for younger individuals, potentially encouraging them to move away from the location.
It's worth noting that the use of such devices has been subject to controversy and debate due to concerns about age discrimination and potential harm to hearing. As a result, the presence and use of these devices vary in different regions, and some jurisdictions have even banned their usage.
If you have personally experienced a high-pitched sound in a department store, it's possible that you encountered a mosquito device. However, without further information, it's challenging to determine the exact cause of the sound you heard.