Related Clues:
- Pop-up, sometimes
- Like a good guard dogs
- Fit for sentry duty
- One may precede a spoiler
- Spoiler ___ (disclaimer before telling someone that Walt kills Jesse then himself in the last episode of 'Breaking Bad,' say)
- Google ___ (notification I get every time Justin Bieber does anything)
- Not asleep at the wheel
- It can be red or amber
- Ready for sentry duty
- Warning providing by dealer trading
- Bitter winter frost ends, sharp
- See 134-Across
- Paying full attention
- Issue a warning to
- Like the best guard dogs