A safety device comprises an electronic circuit (2, 3, 4) including an antenna (6) to detect the presence of a radiofrequency (RF) signal of a predetermined character within a predetermined range of the antenna. A deterring device (12) is responsive to such detection in a manner effective to be a deterrent to transmissions of signals of the predetermined character. In an advantageous application, the radiofrequency signal is a mobile or cellular telephone signal.
