Both options should be complimentary to vibration. But best would be light and unique vibration. This way you can detect it no matter what you are doing.
Indeed. I can feel the noise from those loud building type smoke alarms, that schools and govt buildings install all the time. Household smoke alarms are pretty puny tho, I don't usually feel those unless I'm paying attention. They are such a high frequency they don't vibrate in my body much, and are not very loud comparatively.. (since they only have a 9V battery for power)