And now Harvey knew where the click came from. It came from inside his oxygen pack.
Almost instantly, he felt the soft flow of the oxygen through the tubes. He sat down. Brace sat down heavily beside him. "Those posts," Harvey said. "He must have them all around the hill. They throw out a radio wave that shuts these things off when you go past them." He shook his head ruefully. "I should have guessed it. When I first took a look inside this oxygen pack, I noticed something that looked like a transistor, but I couldn't imagine what that could have to do with oxygen."
Brace let out a long breath. "We should have kept going," he said bitterly.
"There was a good two hours of climbing ahead of us. We'd have been dead a long time before we got there."
"Okay," Brace said. "Let's go wreck these radio