Ambient Assisted Living is pushing the development of innovative wireless monitoring solutions. Most of the available solutions are based on well known wireless communication standards, such as Wi-Fi, Bluetooth or ZigBee. Moreover, there are also a few proprietary solutions, including those designed specifically for biomedical monitoring applications. The success of those solutions depends on many factors, and power autonomy is one key issue, since system recharging requires the user to temporarily remove the device. In this paper, we evaluate the autonomy of three different wireless modules, proposed for use on Ambient Assisted Living applications. We present the measured and expected autonomy for modules built from off-the-shelf components to assess its suitability for real scenario applications. From the results, it is evident that may be worthless to design extremely low power acquisition electronics, sacrificing the acquisition performance, when the main power consumption comes from the wireless subsystem that, which is one order of magnitude higher.