Detective Chief Superintendent Simon Letchford, Territorial Policing crime lead for the Met, said:
"Many of these phones and other devices are worth hundreds of pounds and not only contain personal information but may also have photographs of sentimental value that can't easily be replaced.
"People need to take as much care of their phones in the same way as they would their other valuables. They would be reluctant for example to openly display hundreds of pounds worth of cash in the street.
"There are a number of practical steps you can take to help protect against theft of your phone and which will give us the best chance in the event of a robbery or theft of getting it back for you. I would urge all owners to take the time to carry these out."
The people in this footage are in no way connected to the crimes mentioned by the Met.
More top news
The Metropolitan Police said the building material was found in the force's former training facilities.
The toddler was seriously injured when one of the cars rolled and trapped him between the vehicles in a private car park
The millionaire winner is one of 10 lucky players from the EuroMillions Mega Friday draw on 28 November.