Wearable devices have recently become popular, and more and more people now buy and wear these devices to obtain health-related services. However, as wearable device technology quickly advances, its security cannot keep up with the speed of its development. As a result, it is highly likely for the devices to have severe vulnerabilities. Moreover, because these wearable devices are usually light-weight, they delegate a large portion of their operations as well as permissions to a software gateways on computers or smartphones, which put users at high risk if there are vulnerabilities in these gateways. In order to validate this claim, we analyzed three devices as a case study and found a total 17 vulnerabilities in them. We verified that an adversary can utilize these vulnerabilities to compromise the software gateway and take over a victim’s computers and smartphones. We also suggest possible mitigation to improve the security of wearable devices.