Notifications are an integral part of how smartphones are used today. Apps can use notifications to inform the user about new text messages, upcoming events or available updates. By using visual cues, auditory signals and tactile output the attention of the user can be gained, enabling him or her to react right away. Notifications on desktop computers existed years before the introduction of smartphones and tablets are already widespread and share most of their characteristics. Other types of connected devices will soon join or already have joined smartphones in daily life. Recent development in the field of wearable devices indicates an upcoming widespread adoption of smartwatches and smartglasses. These devices can be used in situations where the use of a smartphone would be impractical or inappropriate. Previous work showed that notifications can distract the user, inducing stress and anxiety. Such effects could worsen with a growing number of notifying devices. Therefore, it is necessary to explore how notifications should behave in this “multi-device” environment. For that reason, we developed a concept for a framework that allows synchronizing notifications across multiple devices, including smartphones, tablets and desktop computers. Based on the approach of research in the large, we implemented the framework with support for a large number of devices as an update to an existing application and deployed it to a user base of several thousand users. After two months in the wild, the updated application was actively used by more than 33,000 users. On a per app basis the application allows disabling the content or sending notifications altogether. We analyzed the user settings for over 36,000 apps and found, for example, that apps from the "tools" category were excluded from sending notifications most frequently. On the other hand, the users disabled sending the text for apps related to communication most often. In a final large-scale study, the users rated the usefulness of synchronized notifications on different devices. Overall, synchronized notifications from messenger apps received the highest usefulness rating across all devices. The gained insights can support the development of ubiquitous notification mechanisms that keep users informed without overloading them.