I was recently told that the common 120V electric receptacles (non-GFCI) found in North American homes can be extremely dangerous to measure using a multimeter. FYI, this came up while I was checking proper connectivity of the wiring directly using the three-prong outlet slots.
The specific concern is not that the operator will mistake hot, neutral or ground slots and stick the multimeter leads into the wrong slot(s). Rather, the stated concern was that the internals of an electric receptacle are not completely isolated from each other and by sticking a single lead into one of the slots, the operator may actually short two or more of these (e.g. Sticking a prong into the ground slot may result in the lead touching both ground and also either hot or neutral).
I am a DIY hobbiest that enjoys upgrading my home for smart components. This warning about the internal structure of a basic electric receptacle set off many warning flags. It's hard for me to imagine that this would be true due to the potential danger but I do not understand how these common electric receptacles have evolved over the last 60 years. Maybe way back in the day there were outlets where this actually was a concern. I hope that this is not possible in modern day receptacles but this is where I'd love to lean on this forum to help set me straight!