“Countdown” is for those horror fans who like their drinks straight, no chaser.

Nothing too fancy. Not too much “explaining,” none that has to make any sense, anyway.

Nice and cheap (a $6.5 million budget). Cast good-looking unknowns (Elizabeth Lail, Jordan Calloway), save for the creepy doctor (Peter Facinelli of “Nurse Jackie”).

Use comics in key supporting roles, for laughs — the cell phone repair whiz (Tom Segura), the geek priest who got into the Holy Catholic Church for the Latin and the demonology (P.J. Byrne).

Get your jolts, and this one is “jolty” in the extreme, the old-fashioned way –shrieking sound effects (including a ring tone), abrupt, shocking edits, and shadows.

Effects? Yank somebody out of the frame — across the floor, or up to the ceiling.

And hire the right master of the macabre to design your creature costumes, makeup and effects. Here, it’s Ehsan Bigloo, who conjures up assorted wraiths, demonic corpses and a genuinely chilling Grim Reaper, cape and cowl, Satanic hands, everything but the scythe.

First-time feature writer-and-director Justin Dec makes the jump from “miscellaneous crew” credits with this latest variation of “the killer app,” a horror subgenre involving the cell phone as harbinger of death (“One Missed Call,” “Cell,” etc.).

Here, it’s a new “Countdown” app that has all the kids abuzz.

“If you could know exactly when you’re going to die, would you WANT to know?”

You know “kids.” Sure. Download that bad boy. “Accept” that “User Agreement.” “Fine print?”  Who has time to read anything longer than a tweet?

Some get the good news of lives of great longevity. Others? Days. Hours. Tick tick tick tick…

“Countdown” doesn’t just count you down to your untimely demise. It all but takes over your phone. It’s malware you seemingly can’t delete — like MacAfee, only free.

And it hits you with these shrieking, insistent “alerts.” Especially when you try to alter your fate by cancelling a trip, ducking out of a car whose driver is drunk, etc.

If we learned nothing else from the “Final Destination” franchise, it’s that “death’s grand design” will not be thwarted. Dodge a drunk driver here, get yanked into the air and dropped on a tub there.

Elizabeth Lail is a nurse whose patient, grimly awaiting his “Countdown” clock to wind down, probably in surgery, convinces her to offhandedly add this new app and unthinkingly click “accept.”

When the patient dies — a prologue sets up”the app that decides when you die inevitability” — Nurse Quinn, Medicine Woman has a moment of doubt. She won’t reach “worry” and “panic” until later.

The tech-nerd cell phone “doctor” (Segura) is awfully droll about how Quinn, and another panicky customer (Jordan Calloway) have been suckered in to this obviously fake app designed to scare the life out of you. But Quinn and Matt are seeing things. And people are dying.

It takes two priests, one referring them to another, the demon “expert,” to get some answers.

“The Bible is like, the ULTIMATE graphic novel!” Father John (Byrne) enthuses. Best line of the movie. Demons in chapter after chapter, descriptions, myth and apocrypha thrown in.

There’s a #MeToo set up, with a creeper doctor (Facinelli), and attacks that the new couple, bound by the shared threat, face together, along with demonology-based “solutions” and an ending that isn’t the worst “How do we write a way out of this?” I’ve seen.

It’s not highbrow entertainment. Movies like this always feel “designed,” like a theme park ride — story beat, JOLT, exposition exposition JOLT, etc. But “Countdown” manages the bare minimum — the occasional shock, characters we root for, thanks to the actors playing them, and situations fraught enough that the audience is talking back to the screen.

MPAA Rating:  PG-13 for terror, violence, bloody images, suggestive material, language and thematic elements

Cast:  Elizabeth Lail, Jordan Calloway, Talitha Eliana Bateman, Peter Facinelli, with P.J. Byrne and Tom Segura

Credits: Written and directed by Justin Dec.  An STX release.

Running time: 1:30