Using smartphones to squeeze in more work at night leads to lower engagement at work the next day at work, via lost sleep, reports Harvard Business Review.

In our second study, we had 161 employees from a broad variety of occupations (both managers and non-managers) complete the same set of surveys, with the addition of measures of late-night usage of television, laptop computers, and tablets. The harmful effects of smartphones on sleep and work engagement held even after accounting for these other electronic devices. Indeed, out of all those devices, smartphones were associated with the most powerful effects.