Embodiments of the present invention provide a method, a device, and a system for detecting device power. The method for detecting device power according to the present invention includes: detecting, by a monitoring terminal, power information of a monitored device; setting a monitoring time interval according to the power information and a preset time interval; and detecting the power information of the monitored device according to the monitoring time interval. The embodiments of the present invention implement that a time interval between next detection and current detection is determined according to detected power information, which can fully save resources without affecting use of a user.