An alarm must have sounded in Patrick Graham’s ear.

After weeks of downplaying the recurring struggles of the Giants defense and issuing reminders that it was early in a marathon season, the coordinator changed to a now-or-never tune. Allowing 515 yards — the single-game high against the Giants since 2015 — and seven scoring drives in a loss to the Cowboys will have that effect.

“In terms of the yardage given up and the loss of the game, it’s unacceptable. Period,” Graham said before Thursday’s practice. “We get paid — myself included — to win games. I’m in this position to help win games. When you give up 500-plus yards in offense, that’s not usually winning football, so it’s completely unacceptable. Completely unacceptable.”

With high expectations coming into the season, the Giants rank No. 29 in total defense, No. 27 in rushing defense, No. 26 in scoring defense and No. 22 in passing defense. Upon deeper dive, they rank No. 29 in percentage of third-down stops, No. 31 in sacks and dead-last No. 32 in opposing quarterbacks’ completion percentage. Plus, there’s an uncanny knack for giving up scoring drives and big plays late in halves.

In other words, the defense does nothing well enough to claim an identity.

“What I have to do, and what we have to do collectively as a group, is look ourselves in the mirror and say, ‘What can we do better?’ ” Graham said.

The answer is simple: Everything. The timeline is scary: The Rams come to town Sunday with an offense ranked No. 9 in total yardage, No. 2 in passing yardage and No. 8 in points per game.

“After performances like that, and now you’ve got the Rams coming in here,” Graham said, “we’re going to find out [what we’re made of]. I mean, we’re going to find out. It’s time. I’m starting with me first. We have to find out. We have to get up there and stop the run — that’s the goal for Sunday — and we have to minimize what they do on Sunday. We have to find out.”

Unlike an injury-plagued offense, the Giants have their highly paid key defensive pieces in place, with the exception of inside linebacker Blake Martinez.

“I definitely think guys aren’t proud of their performance,” safety Logan Ryan said. “You still have to get ready to put your best foot forward this week. Whatever the words may be, I think there is a sense of urgency this week.”

After enjoying career-years in 2020, defensive linemen Leonard Williams and Dexter Lawrence, cornerback James Bradberry and safety Jabrill Peppers have crashed back to Earth. Draft picks Lorenzo Carter, Oshane Ximines and Xavier McKinney have not developed into playmakers. The loss of defensive tackle Dalvin Tomlinson in free agency has been more significant than the addition of cornerback Adoree’ Jackson. Everyone has a hand in the breakdown, even if the culprit changes from one play to the next.

“It’s like when you are trying to play Nintendo and it doesn’t start so you have to blow in it sometimes,” Jackson told The Post. “We have to figure out a way to make sure it always works.”

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After two of their first three losses happened on last-play field goals, the Giants received a wake-up call against the Cowboys.

“You don’t like to lose, especially the fashion that it happened in,” Jackson said. “It really is unacceptable not just with what this organization stands for but for the names on our back, as well. We’ve always been urgent, but it’s one of those things where you hate that it happened how it happened. It’s a punch in the mouth: How are you going to respond to adversity? Either go with it or go against it.”

One of Graham’s solutions could be to acquiesce to some internal suggestions to simplify the scheme, like he did last season.

“How can I make it so we’re playing faster, we’re playing with confidence and everything?” Graham said. “I know this: We have good players. Let me let them play.”

For the Giants, Step 1 for a turnaround is improving the rushing defense after allowing 175 yards per game on the ground to the Saints and Cowboys the past two games.

“We have to find ways to improve it, and it has to start fast,” Graham said. “You’re going to hear from coaches, ‘It’s a passing league.’ The issue is if you don’t minimize the run game or stop the run game early, you’re playing right into the coordinator’s hand. In this league, it’s a recipe for disaster, so that’s the message.”