Interference between passengers' devices and the planes' systems is difficult to gauge and probably rare, experts say, but the possibility of stray signals is stirring anxiety.

It was fragmentary, crazy ... I thought it might have been stray panicked signals from one of the ships under attack.

Hutch's first act was to ask Bill whether he was picking up any stray signals.

"It fills the air with stray signals," Mr. Nakata explained.

Others were the steady stream of chatter coming from ships in the quadrant, personal messages for crew, and stray signals picked up by the sensor array.

"There is one stray infrared signal on Assateague Island."

"It should shield out stray signals."

Their suits' long-range broadcast radio had been put on standby, to make sure nobody who might be listening for such things picked up stray signals.

But ever since we've been on Ararat, we've been picking up the occasional stray signal from other Ultra elements.

One approach, he said, might be an antenna that could be steered to screen out stray signals, or a receiver that could filter them.