Plug-in Modules

If Bluetooth or wireless LAN cards are added as plug-in modules, care must be taken
if the Bluetooth or wireless LAN card relies on the host device for power. This would
seriously compromise a PDA running on two AA batteries.
Plug-in cards come in three thicknesses—Type I cards are 3.5 mm deep, Type II are
5 mm deep, and Type III are 10.5 mm deep—usually too deep to be compatible with
most PDAs.
Present products being sampled include integrated wireless LAN/Bluetooth, wireless
LAN cards from Intersil, and integrated GPRS and Bluetooth wireless cards—the
example shown in Figure 15.1 is by Plextek Limited in the United Kingdom.
Local area connectivity can, of course, include wireless headsets. A common application
is where a user has a handset connected to his or her belt with Bluetooth connectivity
to an earpiece.

Going cordless has its advantages and disadvantages. The advantages are fairly
obvious: no cord to get tangled. The disadvantages include the need to worry about
two sets of batteries (one in the handset, one in the headset) and RF and application
layer compatibility between different vendors. The jury is still out as to whether consistent
headset-to-handset RF and application layer connectivity can be achieved.
Headsets are, however, an example of personal networks in which various devices
are carried on the body—or sewn into clothing—with each device having the capability
to communicate or fulfill a particular function—for example, heart-rate monitoring.
Heart-rate information may have medical value (astronauts in space), competitive
value (knowing how calm a racing driver is), or entertainment value (the pulse rate of
a football or baseball player after they have scored).