we’d need an alarm for device_class to have binary_sensors template show mdi:alarm and mdi:alarm-off,
and for timer:
to create a nice interface to the google home integration for timers and alarms provided by the googlehome component, and others of course.
please consider adding these 2 classes?
(not sure if this list https://www.home-assistant.io/components/binary_sensor/#device-class is complete, but tried and no alarm icon appeared). no listing either on https://github.com/home-assistant/home-assistant/blob/dev/homeassistant/components/binary_sensor/init.py