Waterproof IP44, Current 100mAh, Adapter USB 5V 1000mAh, Lighting power 2W, Type of battery 18650 battery, Battery Life 500 times, Power 5W, Mosquito killing power 3W, Charging time 3hours.
Just check coupons out (with price alert and history). Do you want to know what the best price is?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): 3628ea, e2bcea, TTxBG10, BGOD1, 2019SPEDM, AFfbG10, 0e7f33, BGTS204, FBCOUPON1, BGTRIP01, BGZPBC15, BGTY704CP, BGCuponation10, BGHONEY2110, BG10OFFAFF, BGwhielabel, 13f142, BG10OFFAFF1, BG4d9120, BGAlerabatod, BGAlerabatdo, 00c906, BG00c906, BGe46870
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi DYT-90 Mosquito Killer Lamp. The lowest price was: $15.59.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).