Any ideas here. When Mrs old lady turns on the bathroom light (flouresecent medicine cabinet light) the outside motion sensor light will come on (not always but often). Same lighting circuit.
Ok I'll listen now!

Mrs. Old Lady's bathroom light is 1)ungrounded, or 2) grounded to the neutral, Maybe 3) Starters going bad if it's that old.

poltergiest?

Is it an electronic ballast? Some of the circuitry in those PIR motion sensors isn't very well protected against noise on the line.

If it's one of those lights that can be turned on, off, and reset by flipping the light switch off, waiting the proper amount of time, and flipping it back on, these things are prone to react to anything else on the circuit.

I don't know a fix other than to pick a different style of floodlight.

How old is the house.
Did someone miswire the bath switch to the effect that when the switch is turned on it energizes 2 or 3 loads (improper pigtailing)If the motion detector is wired to the load side of the bath switch, it will come on when the bath light comes on, but only if it's own switch is closed.

Sounds like an interference problem...I once had a "gfci tripping" call that turned out to be caused by a dining room dimmer switch. It didn't consistently trip out the gfci. It depended on how quickly the dimmer was operated.
Try a new starter for the medicine cabinet light?

I know this will sound silly, but I am thinking towards a few simple things such as:

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[*]Is there a Mirror which may possibly be reflecting Infrared Light towards the PIR sensor?,

[*]Is the PIR sensor aimed directly towards a window for this room?,

[*]Is the sensor Tweeked to the limits - such as highest sensitivity and farthest range,

[*]Could the lady be scarring a Cat when she turns on the light - thus making the Cat run away?,

[*]Could the lady simply not realise that the PIR controlled lights were on before she turned on the others?

[*]Could the Wind be responsible for false triggering the PIR sensor? - like blowing trees / leaves and reflecting Infrared light.

[*]Have Mulder and Scully been called out to check into this yet?...had to throw that one out!
</OL>

If these simple methods do not yield results, try analysing the circuit[s], then call for an exorcist

Scott S.E.T.

Hey, Scott...


That is really "thinking out of the box".
Excellent!

Thanks Rojo-Sy!

Escott,
Did this ever get fixed / explained / exorcised?

Scott S.E.T.

I am waiting for a call back for some other work. I have a feeling it might be a while. Thanks for all the replies.