ST201A Fetal Doppler Rechargeable Lithium batteryHigh sensitive doppler probeEasy and convenient to operateFHR numerical and waveform color LCD displayBuilt-in speaker, external earphone socketPatented design with high-class polished finish SpecificationFHR Measuring Range: 50240BPMaccuracy 1% or 1BPM(BPM: beat per minute)Probe Frequency: 2.5MHzUltrasound Output Power: < 40mWNegative Peak Sound Pressure: < 0.2MPaSensitivity: >90dBWorking Mode: Continuous wave dopplerEffective Radiating Area of Transducer: 230mm210Auto Shut-off: After 2 minutes no signal, power off automaticallyDimension: 140 mmL x100mmWx28 mmHWeight: About 150gexcluding batteries