3 Star Inc ADV1009 Radio Shack Advantage Quick and Easy Pocket Phone Line Tester
This RJ11 Jack Phone line tester will quickly test for polarity, and other Telephone line conditions. Use after new phone line installations or when troubleshooting your existing phone lines. Not for use on phone systems (premise switches) or Data. Light-weight, clips to your Pocket without even knowing it's there. Line Powered, no battery needed.
Note: This Radio Shack Pocket Telephone Jack tester is the quickest way I know of to help diagnose problems down to the Demarc (the little Grey Phone Box outside) to determine whether the Fault is in my wiring, or if I need to call the Phone Company to fix theirs. I use it all the time to quickly check my Jacks after I get through Jacking out a Job for a Telco install. Yeah, there's more extensive and expensive testers to tell me all kinds of stuff, but when I just want to know if there's service to a RJ11 Jack, this is the Fastest.