The disruptive nature of smartphone notifications and their negative impact on users’ productivity are well documented. The majority of these results either originate from controlled laboratory studies, or protocols relying on subjective self-reporting, reducing their ecological validity. This paper presents results from a full day in situ study investigating the impact of perceiving one’s smartphone notifications on wrist motion patterns. Through this objective behavioral assessment, we document for the first time the manifestations of notification-induced disruption outside of the lab, independently of user activity and without the need for self-reporting. We identified a decrease in wrist motion activity following the presentation of a notification while the participant was engaged in higher intensity activities, independently of whether the notification is immediately attended to. These findings provide objective support for the claim that notifications have as much potential for disruption when merely perceived as they do when the user actually responds to them.