AG 21B is a high quality pocket size. Foetal Doppler is specially leading to cater to the strict requirements of obstetrician and maternity assistant. Key Aspects Changes Problemsl: It changes the common problems of small models such as low sensitivity, poor sound effect and poor battery cruising power. Suitable Early: It is especially suitable for the early pregnancy foetal heart rate inspection, which can detect the foetal heart rate as soon as foetal heart formed . Voice Effect: Voice and the effect of the sensitivity are equivalent to a desktop, but the appearance is a palm type, it is a very classical combination product. Special Improvements: We did some special improvements on our product.