You're just burning us up with these questions today

I was going to say "something like a sneeze guard, but for the stove" but I like Ken's answer better.

To add to Barbara's answer - I believe the ADA started this second level of protection so that if the hot water heater wasn't set properly, those who cannot feel their extremities (or other parts of their bodies), aren't burned in the shower.  It has become code now in many, if not all, states.

this is a protective valve installed at the point of use like a sink, tub, shower.... not to be confused with a mixing valve that is installed at the hot water tank point.... two different valves.... 

Something to protect from hot water splashing.

I think Barbara Todaro has the right answer.

Yet another burning question -- I see you have your answer already.  The AR membership is quite bright and often clever.  

It limits the amount of hot water that can come through a faucet. 

Ken answered.

A device that protects / defends against scalding hot water. 

Ouch, the water is too hot - turn the Scald Guard!

Don't know this one.

I thing every home needs security.

Keeps you from getting too hot or burned!

An adjustment to not get a burn while showering; cheaper than sun block!