![[article image]](https://cacm.acm.org/system/assets/0003/5593/092019_CACMpg28_Multi-Device-Digital1.large.jpg?1569244741&1569244741 "man slicing fruit on kitchen cutting board")
The use of multiple digital devices to support people's daily activities has long been discussed.11 The majority of U.S. residents own multiple electronic devices, such as smart-phones, smart wearable devices, tablets, and desktop, or laptop computers. Multi-device experiences (MDXs) spanning multiple devices simultaneously are viable for many individuals. Each device has unique strengths in aspects such as display, compute, portability, sensing, communications, and input. Despite the potential to utilize the portfolio of devices at their disposal, people typically use just one device per task; meaning they may need to make compromises in the tasks they attempt or may underperform at the task at hand. It also means the support that digital assistants such as Amazon Alexa, Google Assistant, or Microsoft Cortana can offer is limited to what is possible on the current device. The rise of cloud services, coupled with increased ownership of multiple devices, creates opportunities for digital assistants to provide improved task completion guidance.
Case for Multi-Device Digital Assistance
Arguments in favor of multi-device support are not new. Cross-device experiences (CDXs) and MDXs have been discussed in the literature on interaction design, human factors, and pervasive and ubiquitous computing.2,8 CDXs have focused on scenarios such as commanding (remote control), casting (displaying content from one device on another device), and task continuation (pausing and resuming tasks over time). In CDXs, devices are often used sequentially (that is, device A then device B) and are chosen based on their suitability and availability. Tools such as the Alexa Presentation Language (APL) enable developers to create experiences for different device types (that is, A or B). In MDXs, different devices are used simultaneously for task completion (that is, A and B). Digital assistants can capitalize on the complementary input and output capabilities of multiple devices for new "better together" experiences.