These are devices that jam/interfere with speed detection devices operated by police officers, thereby preventing them from taking a reading. These devices are unlawful and you could face prosecution for perverting the course of justice, which carries a maximum sentence of life imprisonment or obstructing the police.
Devices that only provide information about camera site locations are lawful in the UK. However, note that if you go abroad even these types of detectors may be unlawful. You will need to check what the legislation is in the country you are travelling to.
The government is considering legislation to make it unlawful to use other types of speed detectors but as yet nothing has been finalised.