I can't help wondering if it was connected to the extensive correspondence between David Payne and Mark Warner relating to the group being housed close to each other and to the dining facilities. The upshot of which was that they were able to decide before leaving the UK that they would operate their own listening service.
That suggests prior knowledge of the location of their apartments and the proximity of one of the restaurants, because some apartments are quite far away from the restaurants.
Before leaving the UK is an interesting thought, but how valid is it?
The Paynes had a baby monitor that worked at the relevant distance. One lot of other parents had a baby monitor they did not trust. Two of the families do not appear to have attempted a baby monitor.
So, wind back to 2007 technology and cost. What was the operating range of baby monitors in 2007? So far, I have got claims of 75m minimum to around 200m max, all at prices cheaper than hiring a nanny for a week.
The Paynes monitor
appears to have done the trick, so why didn't the other 3 families cough up for a 2007 spec monitor? Was it because they didn't know how close they would be?
This bit has intrigued me because there is/was an electrical goods shop in Rua Helena Nascimento Baptista, that might or might not in 2007 have flogged baby monitors that worked for Tapas diners. Just a tad difficult to work out what its 2007 stock was, though.