Straphangers jittery over several recent subway slashings should holster their smartphones and pay more attention to their surroundings, the head of the city detectives’ union said Sunday.

Detectives’ Endowment Association President Michael Palladino described the recent spate of knife attacks as “definitely disturbing” and added that subway riders should watch their backs to avoid becoming the next victim.

“Most of the slashing suspects use the element of surprise, and they come up behind you,” he said on John Catsimatidis’s radio show. “The randomness is what concerns me the most because it’s so difficult to police random behavior.”

Getting sucked into smartphones while riding the rails is also a practice travelers should be mindful of — especially as they have come to feel more “safe and comfortable on the subways” over the past 15 years, he said.

“You need to watch what’s going on around you,” Palladino said. “With the recent violence, I think riders have to be more cautious because you can become an easy target if your attention is diverted to your cell phone.”

Palladino added that the NYPD could start considering placing undercover decoys on the trains to lure in potential assailants.

Palladino also offered some more pointed advice to the Black Lives Matter movement and Beyonce, criticizing her for her Super Bowl halftime show.

“To me, all lives matter. Beyonce’s message about Black Lives Matter, in my opinion of course, was misdirected. She should direct her message where it’s needed the most, and that’s in the ‘hood, because that’s where it all takes place,” he said.

“If the Black Lives Matter movement really wants to make a difference, they should pour the medicine directly on the wound. Get into the ghetto, the ‘hood [and] get to the bottom of why people of color prey on other people of color in their own neighborhoods.”