I was watching some videos from the Home Assistant Conference, and I learned a few things about the Home Assistant Android Companion App.
I learned that the app can send the phone's next alarm time to Home Assistant where you can write automations to respond to it. I wrote a simple automation to turn on a lamp when my alarm goes off:
alias: Turn on bedroom lamp when Eric's alarm triggers description: '' trigger: - platform: time at: sensor.eric_s_pixel_3a_xl_next_alarm condition:  action: - type: turn_on device_id: 46863ec32fbfe7b7cf5712d92b1c7db8 entity_id: switch.jasco_products_28169_plug_in_one_outlet_smart_switch_switch domain: switch mode: single
I also learned that the app integrates with the power button menu. When you long-press the phone's power button a special screen comes up that lets you reboot the phone, but it also has a section at the bottom for controlling smart home devices. You can add buttons to trigger scenes, or turn on/off individual devices. Here's how mine looks: