Simply connect in parallel with phone line, powerful led flashes when phone rings. Tthe unit will feature a relay output if connected to a 12VDC power supply, relay output: continuous or on/off to the rhythm of ringing of the telephone. Complete with enclosure. Great for noisy environments, for the hearing impaired, as addional ringer, to replace existing ringer. Accepts standard adaptor & telephone plug, includes: attractive enclosure, adhesive strips for easy fixing.