The setting for the alarm is actually independent from the rest of the phone volumes. When you go the set the alarm and get to the alarm sound list, use the volume rocker on the side of the phone to set the alarm volume.
For some reason, the Hero has a habit of screwing around with the volumes for the alarm. It happened to me a few times where my alarm got muted.
Answers & Comments
The setting for the alarm is actually independent from the rest of the phone volumes. When you go the set the alarm and get to the alarm sound list, use the volume rocker on the side of the phone to set the alarm volume.
For some reason, the Hero has a habit of screwing around with the volumes for the alarm. It happened to me a few times where my alarm got muted.
Thanks for looking and good luck.