Jerrybox MR01 Portable Mosquito Repellent Ultrasonic Wave Technology, Safe, Lightweight Portable Mosquito Repeller, Bug Zapper Effective: Adopts the Ultrasonic Wave Technology; efficiently irritates and drives away most mosquitos; provides long lasting protection(For forest, it's better to use it with a repel spray in some areas which have too many mosquitos) Portable: As small as your index finger; needs only one 1.5V AA battery (not included); designed to be lightweight, attractive and exquisite; multiple languages user manual Convenient: Attachable with a small clip; easy to clamp to your clothes or neckline, or simply put it into your pocket Safe: Produces low-frequency audible sonic waves; safe for both humans and pets; feel relieved to use this non-toxic alternative Disclaimer: The repellent drives away the mosquitos with the Ultrasonic Wave so the sound you hear is normal and it means it's working