A shout above the crowd or a wave of the arm doesn't look like much.

But what happens small subtlety to many is an extension of the communication that helps Vikings safeties Harrison Smith and Andrew Sendejo stay in touch amidst the pre-snap frenzy in the NFL.

The pair of defensive backs roam the secondary on game days for Head Coach Mike Zimmer's defense, rarely in the same place but always knowing where the other is.

They say that comes from extensive film study, an area they've ingrained into their preparation, using technology to connect outside of the team's headquarters.

"Usually during the week while we're studying or prepping, if I see a play or Harry sees a play that could potentially give us some problems, we'll video it and send it to each other," Sendejo said. "We'll say, 'Well how do you see us playing this versus this coverage,' or, 'What would you do in this?'

"Sometimes I'm watching a certain game, and he's watching a certain game and we see stuff that the other doesn't see," he added. "We just kind of send it to each other and figure it out then or the next day we'll talk about it."

Smith, who earned his first Pro Bowl selection in 2015, said the communication has grown in recent years. Both players signed a multiyear extension this offseason.

"It's gotten more and more (frequent) the more we've played together because it's hard to watch every play of the team you're playing," Smith said. "We don't sit there and say, 'I'll watch this and you watch this.'

"We talk through what we're going to do with it," he added. "It really helps because it keeps you one step ahead."

Zimmer has noticed how well Smith and Sendejo have worked together.

"I think they communicate well," Zimmer said. "Almost all the time they're in the right place.

"They help a lot of guys get lined up," he added. "They play real hard and physical so it's been a good tandem."

The duo first met in 2012, when Smith was a first-round pick out of the University of Notre Dame. Sendejo, an undrafted free agent out of Rice University, had just completed his first season in Purple.

They didn't play together much at first as Sendejo worked his way up from key special teams contributor to starting at safety last season.

Along the way, Smith and Sendejo have formed a bond and a trust that is nearly unbreakable.

The results have been there, too.

Although Smith and Sendejo each missed a few games due to injuries in 2015, they started 11 games next to each other. Add in the first three games of the 2016 season, and the Vikings have compiled an impressive *13-2 *record when the duo started next to each other in the secondary.

They also helped anchor a defense that allowed just 18.9 points per game last season, good for fifth in the league.

"We both hold each other accountable," Sendejo said. "We both know the work that the other puts in during the week to be prepared for the game.

"I know that when I need help from Harry on a certain coverage, I know he's going to be there, and he knows that I'm going to be there," he added. "It allows us to play well together."

Smith said their connection stems from practices, meetings and games. But the quick text messages during a week of game-planning also come in handy.

"If we're not on the same page, it's not going to be good," Smith said. "There's time where I'll be stuck, and he'll say something and get me in the right spot.

"Stuff like that happens a lot because the game is so fast," he added. "Things happen so quick so you have to have both of us keeping each other in check."

Smith and Sendejo's bond has even branched out to non-football activities.

Smith is involved with Big Brothers Big Sisters of the Twin Cities and hosts an annual kickball game for "Bigs" and "Littles" at Winter Park.

Likewise, Smith had Sendejo's back in June when Sendejo rappelled down a 38-story building in Austin, Texas, to raise funds and awareness for the Make-A-Wish Foundation.

"Somebody had to be there in case he fell off," Smith quipped. "But it was pretty cool, him hanging off a side of a building."

The friendship between the safeties also extends to other defensive backs. Smith and Sendejo showed up to support Vikings cornerback Xavier Rhodes at his annual charity bowling event earlier this year.

"Just showing up for each other … offense, defense, whatever, but especially within the DB room," Smith said. "You've got to have that (support system) back there because you're going to go through adversity.

"You've got to stick together and fight for one another," he added.

Sendejo estimated the pair spends dozens of hours together during the week before going home and keeping in touch with their phones or iPads.

The 29-year-old Sendejo noted he likes to put on some music and study in 30-minute increments to keep his brain fresh.

And since the pair know each other so well, they said they don't need to send long and elaborate messages when getting the other up to speed on a particular coverage, play call or tendency of an opponent.

"A paragraph is way too long," Smith said with a laugh.

Added Sendejo: "It's usually just a video with the coverage. Sometimes it's just the video of a play that could be a potential issue depending on what we have going in that week."

The constant communication all adds up to each other being reliable when called upon during games.

"You're kind of quarterbacking the coverage so to speak," Sendejo said. "It's a pretty complex defense as far as what we have in.

"You have to be able to do your job. If you can't do your job or you don't know what you're supposed to be doing, they're not going to put you on the field," he added. "We have to make a lot of checks and adjustments and get the other guys lined up."

It's not all business all the time for Smith and Sendejo, however. The pair noted they look for humorous moments while watching film that they can point out to each other or one of their teammates.

"We'll also keep each other in check," Smith said. "If something funny happened in a game and it's one of us, we'll send that, too, to make sure we know that we saw the other guy mess up.

"But it could be anybody," he added. "No one is safe."

Neither are opposing offenses, it seems, especially when Smith and Sendejo are hard at work behind the scenes.

"It's not like there is an 'Ah-ha' moment or something like that," Smith said. "It's basic adjustments that once you talk through them, they're simple.

"But if we haven't seen then before, they could trip you up," he added. "They are things we notice that make us play faster."