Smartphones and tablets are an indispensable part of moderncommunication and people spend considerable time interacting with their devices every day. While substantial researchhas been conducted concerning smartphone usage, little isknown about how tablets are used. This paper studies mobiledevice usage characteristics like session length, interactionfrequency, and daily usage in locked and unlocked state withrespect to location context. Based on logs from 1,585 Android devices (470 years of total usage time), we derive andanalyze 23 million usage sessions. We found that devicesremain locked for 60% of the interactions and usage at homeoccurs twice as frequent as at work. With an average of 58interactions per day, smartphones are used twice as often astablets, while tablet sessions are 2.5 times longer, resultingin almost equal aggregated daily usage. We conclude that usage session characteristics differ considerably between tabletsand smartphones.