Let me tell you why this little gadget became my non-negotiable travel companion. During my solo backpacking trip across Thailand, the ZZRUI alarm was the only thing that let me sleep soundly in questionable hostel rooms.

The first night I used it, housekeeping accidentally tried to enter my room at 5am. The 120dB scream made my eardrums vibrate - but more importantly, it made the staff apologize profusely through the door while I laughed in relieved triumph. That piercing sound is NO JOKE.

What surprised me most? Its deceptive simplicity. Just slide it under the door (gap must be 10-35mm), flip the sensitivity to High (always High for me - I want earthquakes to trigger this thing), and boom - instant security system. The rubber base grips tile floors like a gecko, and at 120g, it disappears in my toiletry bag.

Pro tip: The medium setting caused false alarms when neighbors slammed doors, but high sensitivity worked perfectly. Battery lasted my entire 6-week trip, though I did pack spares after reading reviews. Unlike cheaper models, this didn't slide when pushed - the intruder would need to lift the entire door to bypass it.

Now it lives under my apartment door when I'm home alone. That obnoxious siren gives me 10 extra seconds to grab pepper spray or call 911. For peace of mind that fits in your palm, this is worth every cent.