Very puzzling RF question

Thread Starter


Joined Jan 12, 2015

I saw something just now that is puzzling me - a lot. I have one of these:


A CenturyLink C4000 ADSL modem.

This unit was in use in my house until about three months ago, when I switched over to a T-Mobile 5G solution, the C4000 was put on a shelf in my workshop next to its power adapter, it was disconnected obviously, from the adapter and the adapter was wrapped up too, not connected to anything.

Well I've now re-ordered the ADSL service and so wanted to take a photo of the unit's base that has all of the default network names and so on.

As I hovered my phone over the device's base to take the photo, a message came up "Join the CenturyLink 7985 network".

I moved the device away and the message went away, I moved the unit back and the message reappeared.

How is that device able to emit an RF presence when it has been disconnected from power for over three months? There were no wires connected to the unit either.


Joined Jun 17, 2014
Some cameras ask you to press something in order to scan the photo so they wont do it automatically. I am surprised it didnt tell you what it was doing.

For a minute there you must have thought you had made first contact :)


Joined Aug 21, 2017
In the small range it isnt needed a very high power. We laid out the LORA and NORD datta packet transmitters for industrial environment monitoring uses. Average one small battery life span at first is about year and in second over the 3 years. Believe the uninterrupted data-stream takes far more resources but anyway that are the days of even weeks before the battery discharges.