@David-TP my whole setup has been working perfectly for 16 months without any problems.  We bought a new gas leak monitor and the installation instructions were to reset the main E4 unit, so my husband pressed the reset button.  Since then the satellite unit has not worked and just blinks red.  I have tried reinstalling the satellite E4 close to the main unit in the middle of the room, in the next room, half way up the stairs, on the hall landing, but each time it shows a yellow light and then after a bit it just turns flashing red which I understand to mean it won't connect to the main unit (but the app instructions are not given to reset the satellite unit and I have not tried that, but I am assuming doing that is futile?).  The really annoying thing is the unit has sat at my upstairs workstation all this time and not once have my work zoom calls dropped or I have had a problem getting on line, but just resetting the main unit has caused this satellite unit to fail?  I am worried that I am going to have to shell out for a new satellite unit (if you can buy one singly?) and it won't be an E4 so it may not work with my existing main unit?  Is there nothing that can be done to get my satellite unit working again? Thank you.