How Anti-sleep Alarms Work

Let's start with the simplest anti-sleep alarm system, the over-the-ear gadget. This lightweight plastic device has an arm that slips over one ear, like some telephone earpieces or portable headphones do. Once it's on, a sensor inside the case measures the angle from a perpendicular perspective. If the driver is looking straight ahead -- as he or she should -- the alarm measures the angle at zero degrees.

If you've ever fallen asleep on a subway train or in your high school algebra class, you know that your head tends to fall forward as you doze off. You also know that you may stay asleep for a few seconds or a couple of minutes before your head jerks upright and you're awake again. It's annoying on the bus commute home; it's downright dangerous when driving a car. The anti-sleep alarm looks for any indication that the driver's head is tipping forward: When the earpiece senses that the angle has increased from zero to, say, 15 or 30 degrees, it sounds an alarm. Most manufacturers stress that the sound is loud and irritating enough to wake the driver, but not so loud or sudden that he wakes up with a start and yanks on the wheel or steps harder on the gas.

You can easily adjust the angle that triggers the alarm. If you know you can sleep with your head almost upright, you can set your earpiece to a smaller angle. If the alarm goes off every time you bop your head along with the tunes on your radio, then you should set your triggering angle to 30 degrees or more.

While these alarms work to help keep drivers awake, some high-end manufacturers are adding sleep sensors to their cars right at the factory. A few notable systems:

In-car systems can be expensive, especially those that involve in-dash cameras to monitor drivers instead of sensors that are already in place. Read on to find out who can benefit from an anti-sleep alarm, no matter what the cost.

D­rivers are the obvious target market for anti-sleep alarms. Truck drivers with tight schedules often find themselves hauling freight overnight. An alarm worn over the ear and a thermos of coffee could be enough to keep drivers alert without resorting to pharmaceuticals. Even the casual spring break road tripper could use a sleep alarm.

Over-the-ear alarms have uses beyond the driver's seat. A student cramming through the night could skip the usual chemical ways to stay awake and slip an alarm over his or her ear instead. Night security guards, especially those who work in stationary posts and gate houses, could also make use of this simple technology.

While these alarms can keep tired eyes open and brains alert enough to study, driving while sleepy is dangerous. Having a sleep alarm either built into in the car or worn on the ear may give tired drivers a false sense of security. This danger led the Australian state of Victoria to ban the devices in 2007 pending further safety testing.

Anti-sleep alarms would help travelers who'd rather hit the road than the hay, but the best and safest remedy for a driver's drooping eyelids is to stop and take a nap.