Anyone know what this slotted item is for?

[tonype]

I am thinking that is it to allow remote access (insert something in to activate?).

 

[augie47]

A couple on manufacturers make a key switch that looks like that. The keys are somewhat horseshoe shaped.
Here is Leviton's

 

[Dennis Alwon]

I agree, it is a key switch. I have used them on pool lights before to keep kids from playing with it.

 

[infinity]

I agree, there are several versions of a key that will fit this depending on the manufacutrer.

 

[tonype]

Thanks all!