In recent years, growing awareness of the dangers of concussions--whether suffered from military blasts or hard hits on the football field--has spawned advanced helmets that sense dangerous blasts or blows, and even provide custom levels of protection. A new helmet device now senses and warns of another danger that can threaten the lives of soldiers, industrial workers, and athletes: heatstroke.

The system, which is coming to market next month from an Atlanta startup called Hothead Technologies, is initially aimed at football players. Since 2005, heatstroke has killed 33 American football players, most of them high-school students, according to a study carried out by the National Center for Catastrophic Sport Injury Research.

The new device consists of a rugged and highly sensitive sensor encased in a helmet cushion, with the probe pressed against the wearer's forehead in the vicinity of the temporal artery. Temperature readings are beamed to a PDA held by a coach or trainer on the sidelines via a short-range wireless link.

Heatstroke sets in when body temperature hits 106 °F, leading to neurologic dysfunction. In extreme cases, it can lead to death. But an athlete's temperature will often climb above 100 °F and then dip down, so software on the PDA monitors the pattern of temperature change. If the wearer's temperature reaches 102.5 °F and stays there for more than 20 seconds, an alarm goes off. "We're looking for the guy who's hot and isn't cooling down," says Jay Buckalew, Hothead's founder. A database on the PDA stores each player's data, including his temperature readings, medical history, and emergency contact information.

Buckalew, a former communications-equipment salesman and installer, says that he became obsessed with the problem after passing out while installing equipment on a brutally hot rooftop in Puerto Rico several years ago. "It became apparent at that time that we needed a technology that could at least offer an early-warning system," he says. "You get in these closed, confined areas and get hot, and you can black out."

Hothead worked with GE Sensing & Inspection Technologies to develop the temperature sensor and radio-transmitter tag. "What Hothead had worked out was a communications scheme with the coach's PDA, to signal when a player is getting into trouble," says Harry Perrine, a GE engineer who worked on the project. "The biggest challenge was how to isolate a signal that could be indicative of the player's condition with a wide range of variables--you could be playing in Wisconsin, or in Arizona at 100 degrees." The sensor itself uses standard off-the-shelf technology, but it needed to fit within a helmet cushion and survive impacts. "We solved those issues in the packaging," Perrine says.

Hothead's broader goal is to supply heat-sensor devices to military and industrial customers. To do this, the company is working on winning environmental and safety certifications. Meanwhile, Hothead is already tapping the football market, partnering with helmet manufacturer Schutt Sports on a helmet system that costs $99 per player, and will reach the market in April.

Buckalew says that the sensors and radio transmitters can be retrofitted to many kinds of helmet. And the company is developing a headband version that can fit under all kinds of headgear. It may offer individual units that could, for example, deliver warnings directly to marathon runners.

Testing of the device is under way in an academic lab and should be published in a peer-reviewed journal in the coming months, Buckalew says. In the meantime, the company claims that in its own testing, the temperature recorded by the unit is accurate to within 0.5 degrees of the wearer's actual temperature.