Like other Apple devices, your HomePod permits you to set custom alarms.
You can create multiple alarms using just your voice, optionally add some context to them, if you like, and more. Your Siri speaker will signal you when one of your created alarms goes off.
Siri on HomePod allows you to create as many alarms as you want, manage them, remove ones you no longer need, turn specific alarms on or off, create recurring alarms, and more.
Alarms do not synchronize across multiple devices via iCloud. Any alarms created using your HomePod will not appear on your Mac, iPhone, or other devices, and vice versa.