A biocidal composition comprising 2,2-dibromomalonamide and an aldehyde-based biocidal compound, and its use for the control of microorganisms in aqueous and water-containing systems. A motion detector may be provided to turn the lamp off and on when a pet approaches the litter box. The magnetic field is arranged to move the magnetically operated switch from a first configuration to a second configuration. The device may be applied to shielding applications for frequencies ranging from 100 kHz to 10 GHz.