There are six wired smoke detectors installed in my house. I bought six new wired replacement smoke detectors. Turned off the main power switch from electrical box. I don’t detect any current in the black (hot) and white wires: however, the electricity detector beeps when I touch red/yellow communication wire that links/communicates with other installed smoke detectors. Is it safe to touch red/yellow wire to replace smoke detectors? Why is current in red/yellow wire and how much?

 

If you are sure you shut off the breaker and you get the beep from the detectors then:

Just some thoughts -

#1 - If all the detectors are not of the same name brand and sometimes model they can set off signals and beep.

#2 - If you are replacing one at a time without removing all of the old ones then post #1 may be to blame (also see #3 below). Have you removed all the old ones before replacing with new ones?

#3 - If the existing detectors have battery backup then that may be causing them to sound as you replace one at a time and why you detect power in the line with your tester.

#4 - "electricity detector" this may be detecting the low voltage in the line if they have battery backup. What did you use to test if there is power in the hot and neutral wires?

#5 - Are all the new ones you bought of the same brand and model?

 

Remove the backup batteries.

 

Yes all new six smoke detectors are same brand as the old smoke detectors already installed. I used a voltage tester to check the current in the hot black and white wires.
I did not remove batteries from the old smoke detectors maybe that why they have low voltage.
How much low voltage red wire normally have?

Is it OK to touch the red wire after main circuit breaker is shutoff and battery is removed from the old smoke detector? My only concern is getting shock from the red wire. There is no current in black and white wires because circuit breaker is shutoff and I am OK with both touching both black and white wires.

 

Non contact testers if that is what you are using can't measure voltage, only an electromagnetic field which may be meaningless. You probably have no measurable voltage.

 

The red interconnect conductor only carries voltage while the alarm is activated. You should not get a shock from it.