Cable splicing of your own signal is not illegal and there are devices and methods to ensure that your split cables do not diminish your television signal or Internet service. Stealing cable from a neighbor, however, is illegal, and sharing your service is a violation of your cable TV or Internet service agreement. The cable company wants to know about any possible cable theft as it means lost revenue for them and higher bills for honest customers. If your cable has been spliced, possibly by a neighbor stealing your signal, then it would behoove you to discover it quickly.
Note any Changes in your Signal Quality
Look for interference in your television signal. This is indicated by static, pixelation or "ghosting" which is a slightly offset double image of the picture.
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Watch for service hangs—instances where your signal simply pauses for a second or two and then skips to catch up. If this happens frequently it may be an indication that your cable has been spliced.
Use one of the many online tools to determine your connection speed for cable Internet. Check these speeds against the speeds your ISP is providing and note any significant changes. Small fluctuations are normal, but larger changes in your speed may mean someone else is leeching off of your line.
Check the Cable for Signs of Splicing
Look for signs of splitting in the cable lines leading away from your home. This may be difficult to determine as a crafty neighbor could bury the wire or even split it from the pole and not directly from the line connected to your house.
Check all of the wires that lead away from your house for any that are unknown. Make a note of any wires that you do not recognize and where they are located and where they lead.
If you are in an area that uses an NTL box for cable connection, check if there are any wires connected to the box that do not lead to your own home. Any wires connected to the NTL box should lead directly to your home. A wire that has been spliced without your knowledge will most likely lead away from your home.
Ask the Cable Company to Investigate
Call the cable company and have them test your lines. They should be able to determine the dBmV—the unit that your signal is measured in. The measurement is taken by testing the time it takes for a signal to be sent to you and the time it takes the cable company to receive a signal from you. If the signal is diminished, then further investigation may be necessary.
Ask the cable company to send a technician to physically test your lines and check for signs of tampering.
Ask the technician to check your Internet connection setup and router information. If someone is stealing your signal, then you should see the extra users listed in your router information pages.