The Mosquito or Mosquito alarm (marketed as the Beethoven in France and the Swiss-Mosquito in Switzerland) is an electronic device, used for solving loitering problems, which emits an annoying sound with a high frequency. The newest version of the device, launched late in 2008, has two frequency settings, one of approximately 17.4 kHz that can generally be heard only by people under the age of 25, and another at 8 kHz that can be heard by most people. The maximum potential output sound pressure level is stated by the manufacturer to be 108 decibels (dB). The sound can typically only be heard by people below 25 years of age, as the ability to hear high frequencies deteriorates in humans with age (a phenomenon known as presbycusis).

The device is marketed as a safety and security tool for preventing youths from congregating in specific areas. As such, it is promoted to reduce anti-social behaviour such as loitering, graffiti, vandalism, drug abuse, drug distribution, and violence. In the UK, over 3,000 have been sold, mainly for use outside shops and near transport hubs. The device is also sold in Australia, France, Denmark, Italy, Canada and the USA.

The Mosquito has attracted controversy on the basis of human rights. Critics say that it discriminates against young people and infringes their human rights, while supporters argue that making the Mosquito illegal would infringe the human rights of shopkeepers who suffer business losses when "unruly teenagers" drive away their customers. Mosquito distributors have said that they keep standards to ensure that the device is not abused, and Howard Stapleton who invented the device has asked European governments to legislate guidelines governing its use.