Led Lights For Sale Where Can I Find A Phone Line Off-hook Indicator For Sale? Something With An LED Light To Indicate Line In Use

Where can I find a phone line off-hook indicator for sale? Something with an LED light to indicate line in use - led lights for sale

Something very simple, maybe just an LED light in a small plastic box with a battery that has a phone in and out powered bookable (get online), which illuminates when the phone line is used so that no one decreases. It will be used in a number of fax machine with multiple fax machines, so that someone does not start a fax while someone else uses the line.