Using a service offered by a holiday operator is one thing. What the McCanns did was another thing. Why you insist on pretending two different things are the same I don't know - well, I can guess.
Nothing you say alters the fact that those particular children were left alone in an unsafe environment. Not only that, we are expected to believe that their parents didn't notice the hazards.
So YOU are saying that using a listening service provided by an hotel is OK, but doing the same yourself is not OK ?
Gawd strewth Gunit the hotels (and Butlins) did not go into the place, they just listened outside.
The Tapas group actually went into the apartments and observed (altho poor Matt missed looking around the corner at Madeleine). I feel so sorry for that poor guy and for Jane. They have taken some stick !
As for listening devices at reception! They would be a very poor substitution, because as soon as reception got very busy (such as checking a line up of new guests in) the listening devices would very much take a back seat.
I doubt that an abduction using drugs and thru the front door would have been heard or noticed by reception anyway.