"4 pieces per set" Contains: 1 piece Voltage detector for AC: 12V–1000V for high sensitivity and 48–1000V for low sensitivity voltages 50/60 Hz is the frequency. Mode of alarm: both light and sound alarm One piece electronic gas indicators Methane range: 50–1000 ppm Gas detection: flammable gas Sensitivity of response: <50ppm Reaction time: <= 500 ppm: 5 s; >= 500 ppm: 2 s One piece wood moisture gauges: Range of moisture measurement: 0–58% Accuracy of moisture measurement: ±2% One digital temperature and humidity meter: Temperature range: -20°C to 60°C (-4°F to 140°F) Humidity in the air: 0~99% RL Eight Pieces 1.5 volt AAA batteries double blister packaging."