This is a simple-to-use hydrogen gas sensor, suitable for sensing hydrogen concentrations in the air. The MQ-8 can detect hydrogen gas concentrations anywhere from 100-10000ppm. This sensor has a high sensitivity and fast response time. The sensor’s output is an analog 
 
Description
Main chip: the LM393, MQ-8 gas sensor
Working voltage: DC5V
1. With a signal output instructions.
2. Dual signal output (TTL level output and analog output)
3. TTL output valid signal for low level. (When the low output electric signal lights at 4. ordinary times, can be directly pick up SCM)
5. Analog 0 ~ 5 v voltage, the higher the concentration, the higher the voltage.
6. High sensitivity to hydrogen
7. Can be resistant to ethanol steam, LPG (petroleum), smoke interference
8. Has a long service life and reliable stability
9. Quick response recovery features
 
Resources: 
1. MQ-8 Hydrogen Gas Sensor Circuit Built with an Arduino
2. Interfacing MQ-8 Hydrogen Gas Sensor Module with Arduino