Thursday, April 20, 2006

The Active Badge System

The development of the infrared LED in the early 1960s has given rise to a huge number of applications, the most familiar of which is the remote control, and in 1989, researchers at the Cambridge University Computer Laboratory in Cambridge, England, began work on a system that incorporated infrared LEDs into employee identification badges. After roughly four years of work, their research resulted in the development of the "Active Badge."

The basic concept of the Active Badge is straightforward. Employees are given a special identification card equipped with an infrared LED that sends out a unique code every fifteen seconds or so. If the card is within six meters of an infrared sensor (mounted on a wall or ceiling), the code is read by the sensor. The sensor is connected to a network of other sensors, all of which are linked to a central station. The central station periodically retrieves data from each of the sensors and uses the information to compile a map of each badge's current location.

As careful readers have already noted, the most obvious limitation of the Active Badge system is that it tracks badges and not people; it only tracks people if they actually wear or carry the badges, and more specifically, the badges that have been assigned to them. In the view of the designers of the Active Badge, the fact that you can take the badge off is one of the system's advantages:

There will always be some days when for whatever reason somebody does not wish to be located. This is easy to solve because the system tracks badges and not people. Anybody in this situation can easily remove their badge and leave it on a desk. The Active Badge system will now be fooled into concluding that person is somewhere where they are not. This kind of escape mechanism is not an undesirable system feature and may be an important factor in making this system acceptable for common use.

Technically speaking, when an Active Badge is put in a drawer or an employee's pocket, it slowly goes to sleep (as a power-saving measure). The sensor network will continue to display the badge's last known location, but the likelihood of finding the badge at that location (displayed as a probability on the Active Badge information screen) will steadily decrease.

The question for employees is how well such disappearances from the sensor grid will be tolerated by their employers. In a work environment where there is a strong management expectation that employees will wear their Active Badges, periodically taking off the badge and "disappearing" from the sensor system will undoubtedly be perceived as negative behavior. Companies can (and sometime do) impose a requirement that employees wear an Active Badge at all times, but with a technology that immediately raises so many privacy hackles ("Let's see, George, it says here that you spent a total of two hours yesterday in the second floor restroom—are you feeling ok?"), employers are taking a more persuasive approach.

The chief benefit that employers offer in exchange for wearing the Active Badge is a more efficient workplace. The Active Badge system makes it easier to receive phone calls while moving around a building and makes it easier to locate coworkers. Call-routing, of course, is only one of the Active Badge's capabilities. The Active Badge system was designed with the following commands:
  • WITH—a list of the other badges in the same area as the target badge
  • LOOK—a list of badges currently located in a particular area
  • NOTIFY—an alarm that goes off when a particular badge is picked up by the sensor system. (NOTIFY was designed to make it possible to deliver an urgent message to someone who had been out of the building and had just returned. It could be easily modified to sound an alarm when a particular badge enters an area where it is not authorized.)
  • HISTORY—a log of the badge's location over a period of time
When the Active Badge was first developed, the period of history recorded was limited to a single hour, and the information was stored in dynamic memory, not archived to permanent storage. Back in 1992, storage was still quite expensive: roughly $4 per megabyte. By the summer of 2002, you could buy a 160-gigabyte hard drive for $229.98. One hundred sixty gigabytes will hold a lot of Active Badge data.

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