In most cases you do have to
reset & re-install everything.
When batteries are replaced in a sensor, it re-generates a
new security code. This new code will no longer be recognized by the
PS561 until you do an install. Sometimes if you change the batteries fast enough (within a few seconds) you can retain it's code.
Some say that you can wait over 4 hours after replacing batteries and that sensor will re-install itself into the correct location on the
PS561.
I've never tried this since it only takes 5 minutes to walk around the house and press all the test buttons to do a re-install.
Once a sensor generates a new code, I don't see how the
PS561 can recognize it without doing a re-install anyways.
I don't use the
MS10A sensors, but I do use many
DS10A's, and one thing I found I had to do after replacing the batteries is to press & hold the test button for about 10 seconds for it to actually generate a code for itself and be recognizable to the
PS561 when you go to install it.