As the officers walked up to the entrance of a Harlem housing project, a loose knot of people out front scattered into the damp, dark night and a few lingerers cast cold stares at the officers. One of the officers reached into his pocket and pulled out the newest tool in the Police Department’s crime-fighting arsenal: a smartphone.

Officer Tom Donaldson typed in the building’s street address, and with a few taps of the screen, an astounding array of information bloomed in his palm.

The officers suddenly had access to the names of every resident with an open warrant, arrest record or previous police summons; each apartment with a prior domestic incident report; all residents with orders of protection against them; registered gun owners; and the arrest photographs of every parolee in the building. The officers could even find every video surveillance camera, whether mounted at the corner deli or on housing property, that was directed at the building.

“You can see that in this one 14-story building there are thousands and thousands of records,” Officer Donaldson said while canvassing the Lincoln Houses on Park Avenue during a 6 p.m.-to-2:30 a.m. tour starting on Wednesday night.