Even in cool temperatures, cars can heat up to dangerous temperatures very quickly. Even with the windows cracked open, interior temperatures can rise almost 20 degrees Fahrenheit within the first 10 minutes. Anyone left inside is at risk for serious heat-related illnesses or even death. Children who are left unattended in parked cars are at greatest risk for heat stroke, and possibly death.

NEVER LEAVE PETS OR CHILDREN IN PARKED CARS - EVEN WITH THE WINDOWS OPEN. TEMPERATURES INSIDE PARKED CARS CAN REACH 130 DEGREES IN ONLY A FEW MINUTES

The radio pill, part of the CorTemp Physiological Monitoring System manufactured by Palmetto, Fla. based HQ Inc., relies on a temperature-sensitive quartz crystal oscillator whose vibration frequencies are well known for temperatures ranging from ­60 °C to 150 °C. For instance, the crystal oscillates at 262.25 kilohertz at the normal body temperature of 37 °C. The electronic components calculate the temperature and transmit the data as a digital signal. Power comes from a silver oxide hearing aid battery that holds enough energy for nine days of temperature readings. The capsule remains in the body for only 24 to 36 hours before it is eliminated.

The temperature readings are transmitted wirelessly to a handheld receiver­data recorder. As the digital signal induces a voltage on the pill's communication coils, this voltage creates a quasistatic magnetic field with a radius of about a meter. When a coach or trainer holds the receiver to the small of a player's back, a magnetic coupling between the pill and the receiver induces a voltage in the handheld device's antenna, which is then demodulated to retrieve the original temperature data.

Because magnetic communication does not generate a propagating wave and there is strong attenuation of the signal with distance, the data are hard to intercept and virtually free from interference-even if there are dozens of other players running around the practice field with radio pills in their guts. Creating such a magnetic communication bubble also requires very little power, which allowed the radio pill's designers to use the tiniest of commercial batteries.

The players ingest the pill, which transmits their body temperature to a handheld device for about 24 hours or so, after which it’s eliminated from the body. All the hardware involved here ain’t cheap — teams fork over $2,500 apiece for a few data recorders, plus an optional $4,000 handheld that serves as a central monitor for all the players. The bright side is it makes that iPaq hx4700 seem like a steal.