Examples disclosed herein relate to determining a power difference in sensor signals. Examples include a first sensor to transmit a first ultrasonic signal into a pregnant woman and to receive a second ultrasonic signal； and a second sensor to transmit a third ultrasonic signal into the pregnant woman and to receive a fourth ultrasonic signal. A processing resource determines a first power difference of the first sensor according to a difference between respective powers of the first ultrasonic signal and the second ultrasonic signal and is to determine a second power difference of the second sensor according to a difference between respective power of the third ultrasonic signal and the fourth ultrasonic signal. In examples, the processing resource is to determine a relative location of the fetal heart according to a comparison of the first power difference and the second power difference.
