It is not uncommon for a fetal heartbeat doppler to fail in detecting a heartbeat at 11 weeks of pregnancy. The accuracy of the doppler can vary depending on factors such as the position of the baby, the mother's body shape, and the skill of the person using it. In some cases, it may be too early to detect the heartbeat using a doppler. However, if you are concerned, your doctor may recommend further tests such as an ultrasound to confirm the presence of a heartbeat and ensure everything is progressing normally. It's important to remember that every pregnancy is different, and not hearing a heartbeat with a doppler does not necessarily indicate any problems.