M20 Electronic Mosquito Repeller Ultrasonic Mosquito Repellent Bracelet Watch Thermometer
Feature:
Pure physical mosquito repellent, not chemical mosquito repellent;
Safer, more environmentally friendly, more assured and healthier;
The elderly, children, pregnant women and pets can wear it. 
The product can be worn indoors and outdoors (by the sea, parks, camping, etc.) Mountain climbing, fishing.

Specification:
Product model: M20
Product color: Black, White, Pink (Optional)
Input: 5V/1A
Output: 34Hz-70kHz
Battery capacity: 90mAh
Charging time: about 30 minutes
Working time: 150 hours
Function: Ultrasonic mosquito repellent, wrist watch, temperature measurement
Product weight: 50g
Packing size: 45*60*100mm/1.77*2.36*3.94"

Principle of mosquito repellent:
It imitates the sounds that female mosquitoes hate, such as the sounds of male mosquitoes and dragonflies. 
In nature, the annoying mosquitoes are all female mosquitoes, and they are in the stage of conception and egg laying. In this stage, female mosquitoes will avoid male mosquitoes to avoid second conception. So simulating the sound of male mosquitoes can achieve the mosquito repellent effect.

Note:
There may be slight size deviations due to manual measurement, different measuring methods and tools.
The picture may not reflect the actual color of the item because of different photographing light, angle and display monitor.