***** **********Best Quality Guranteed. *****Doesn't Work Alone - Work with receiver M508. This is only for expansion*****Easy to Install - No wire needed. Each receiver can be paired with up to 40 transmitters D017*****LED Indicator - LED indicator creates a visual alert for the hearing impaired*****Useful - The wireless and portable design works well in receptions, home, retail stores and business environments. *****Compatible with other receivers in - M508, M520