They appeared!
The Death Eaters patrolling Hogwarts Castle late at night felt the scorching heat from the magical coins in their hands and realized that Dumbledore's Army had truly emerged from the Room of Requirement, intending to head to the castle dungeons under cover of night to rescue people.
However, just as all the Death Eaters received the alert and were roused to attention, no second alert came for a long while. That meant they had failed to catch anyone, or the enemy had already headed for the dungeons.
Snape had developed this method of passing information based on the method Malfoy had previously provided for Dumbledore's Army.
As for using Communication Bookmarks as a means of communication like the Defense Association, the Death Eaters wanted to as well. But those things clearly could not be made in a short time. Most Death Eaters were better at Dark magic than Transfiguration Charms, and even if they threatened Professor McGonagall into making Communication Bookmarks for them, they might not dare use them.
"It looks like the Death Eaters have spotted us."
Halfway to the castle dungeons, Arthur noticed the red glow beside his watch. He stopped and turned to look at his sons.
"The Death Eaters probably have some means of communication too." Fred and George exchanged glances, unsurprised. "We guessed from the start that this was a trap. Since it's a trap, they must have a fast way to communicate so they can surround us from all sides."
Arthur and Bill were both quite astonished. The Defense Association members remained remarkably calm, as though being discovered by the enemy had been expected all along. They were both curious what this group usually did. How did they seem even more experienced than them?
Perhaps noticing their surprised looks, George chuckled and