Recent mobile sensing applications, especially those
leveraging participatory sensing paradigms, typically use
smart phones as sensors. While smart phones have builtin
GPS and cellular-based communication capabilities, their
battery life is rarely longer than a few days. A typical smart
phone will completely drain its battery in about 6 hours if the
GPS is running continuously [14, 21]. This prevents them
from being used in unattended deployments for long periods
of time.