Receiver: 60mmx 86mmx41mm (W/H/D), RF Modulation: GFSK (Gauss frequency Shift Keying), Frequency band: 2.4GHz (2405-2478MHz), (2.36x 3.3x 1.61 inches), 65mW, 1 KHz, Earphone output level: 32Ω, Battery life: Transmitter: Approx. 3.0 hours, Audio input connector: 3.5mm mini jack, Distortion: 0.1% or less (32Ω, Transmitter: 60mmx 86mmx28mm (W/H/D), RF output level: 2 mW, Signal/Noise: 76dB or more, Power requirements: 1.5V DC (One AA size battery), Consumption power: Transmitter: 1.5V/120 mA, Receiver: 1.5V/120 mA, 65mW output), Receiver: Approx. 3 hours, Reception sensitivity: -85dB +/- 3dB / 0dB=1V/Pa, Frequency response: 35Hz-14KHz±3dB, Transmitter: 136g (4.37oz) (Without battery), Receiver: 152g (4.89oz) (Without battery, Weight: , 1kHz, (2.36x 3.3x 1.1 inches), Dimensions: , Operation range: 25m (80ft.).
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.
Updated: 29-07-2025
Banggood
Warehouse in China.
Link: Boya BY-WM4 Mark II Wireless Microphone System
$80.99 with coupon: BGAFF10OFF
$80.99 with coupon: bGhOnEy10
$80.99 with coupon: bgshOOp10
Additional Banggood coupons:
1. First page
2. Second page
Price history and price alert
Check out price history chart (for all/most countries) for Boya BY-WM4 Mark II Wireless Microphone System. The lowest price was: $78.62.
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)).