No. Rest days never break a streak, and they never use a shield.
A rest day is any day a habit isn't scheduled. If your workout habit is set to Weekdays, Saturday and Sunday are rest days: your streak simply carries over from Friday to Monday.
On a rest day, the habit's card says Rest day. You have two options:
- Skip it. Nothing happens to your streak.
- Do it anyway. Open the habit and tap Check off anyway, or tap the check on its card. It counts as a bonus and adds one to your streak.
To change which days are rest days:
- Open the habit from the Today screen.
- Tap Edit.
- Under Days, choose Every day, Weekdays or Custom, then tap Save.
Heads up: changing the days recalculates the habit's past days under the new schedule, which can change its current streak.