•We examined the effects of smartphone use for work late at night on next day behavior.•Across two experience sampling studies, smartphone use reduced daily work engagement via sleep and depletion.•The effects of smartphone use were unique from those of other technology use. Smartphones have become a prevalent technology as they provide employees with instant access to work-related information and communications outside of the office. Despite these advantages, there may be some costs of smartphone use for work at night. Drawing from ego depletion theory, we examined whether smartphone use depletes employees’ regulatory resources and impairs their engagement at work the following day. Across two studies using experience sampling methodology, we found that smartphone use for work at night increased depletion the next morning via its effects on sleep. Morning depletion in turn diminished daily work engagement. The indirect effects of smartphone use on depletion and engagement the next day were incremental to the effects of other electronic devices (e.g., computer, tablet, and television use). We also found some support that the negative effects of morning depletion on daily work engagement may be buffered by job control, such that depletion impairs work engagement only for employees who experience low job control.