Cell Phone Bombs

How law enforcement can (and can't) prevent them.

Terrorists have long used cellular phones to trigger improvised explosive devices (IEDs) not only on Iraq roadsides, but also in attacks worldwide. Notably, cell phones detonated the bombs that destroyed public transportation in Madrid and London in 2004 and 2005 respectively; terrorists also planned to use them to bomb commercial U.S. flights in August 2006.

Although in the two previous cases, most of the bombs exploded within seconds of each other, one London bomb took nearly an hour to detonate after the initial attacks. This discrepancy has led some law enforcement advocates to conclude that police should be able to use cell phone signal jamming equipment to prevent future attacks.

However, under current federal law, only federal law enforcement agents can use such equipment. Local police fear this isn't enough; they cite, as one major issue, longer-than-desirable federal response times to terrorist incidents or suspected plots. As a result, one vendor has challenged the law.

How terrorists use cell phones

"The remote-control IED is terrorists' first choice of bomb today," says Howard Melamed, chief executive officer of Coral Springs, Florida-based Cell Antenna Corp. "That's because they're so easy to construct and deploy." Bombers use the cell phone as a typical remote control: to send a signal via radio airwaves. The signal energizes a relay connected to a blasting cap, which in turn detonates explosive material.

Although remote controlled toys and keyless entry devices set off bombs too, cell phones remain the most popular. That's because they're convenient in a variety of ways:

  • Using 1200mA x 3.7-12 volts, they have just the right power.
  • They have time synchronization capabilities.
  • They have an extremely accurate alarm clock function.
  • They include a vibration circuit that can be addressed by phone number or function.
  • They allow for worldwide usage.
  • It's impossible to track where they come from and where they go — especially if they're disposable.
  • It's easy to get inside their circuitry.
  • They're easy to conceal.
  • Their highly unstable batteries are easily ignited.

Of these features, two are of crucial importance: the phone's vibration function, and the battery.

The vibration function is the part terrorists use to trigger bombs. "The mechanism consists of a motor with an asymmetrical wheel," Melamed explains. "That's what shakes the phone. A terrorist using it as a trigger simply removes the motor and connects the circuit to the relay or blasting cap." At that point, the terrorist can use the phone's alarm or a simple phone call to trigger the vibration circuit — and thus the bomb. Melamed says terrorists who want to see the explosion often dial the phone.

The cell phone's battery is also critical. "Most cell phones use lithium ion cobalt batteries," Melamed says. "This material is highly unstable. In fact, manufacturers include warnings that the batteries may explode if tampered with or exposed to fire." When a battery shorts, he continues, one of three things happens:

  1. Nothing.
  2. An explosion.
  3. A flame-up, or fire.

Batteries are designed to "fail safe," as Jim Akridge, CEO of Austin, Texas-based Valence Technologies Inc., explains. "Electronic circuits control the rate of energy discharge. Inside the cell casing are two safety devices. One limits the current, and the other limits the pressure build-up. These batteries are designed to shut themselves off if they're shorted externally." Additionally, he says, all batteries are built with strong, hard-to-open cases.

However, Melamed says some illicit batteries made overseas lack these fail-safes. In 2004, manufacturers such as Verizon Wireless and Kyocera Wireless issued recalls for the counterfeit batteries they had unknowingly used in their cell phones. Sony and Nokia now issue documents that warn consumers to use their proprietary batteries for this reason. Terrorists may use "bad" batteries in their bombs — or adapt "good" batteries by overriding their safety circuits.

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