Wireless device pairing is a critical security mechanism to bootstrap the secure communication between two devices without a pre-shared secret. It has been widely used in many Internet of Things (IoT) applications, such as smarthome and smarthealth. Most existing device pairing mechanisms are based on out-of-band channels, e.g., extra sensors or hardware, to validate the location proximity of pairing devices. However, out-of-band channels are not universal on all wireless devices, thus this type of scheme is limited to certain application scenarios or conditions. On the other hand, in-band channel-based device pairing aims at universal applicability by only relying on wireless interfaces. Existing in-band channel-based pairing schemes either require multiple antennas separated in a good distance on one pairing devices which is not applicable in certain scenarios, or require users to repeat multiple sweeps which is not optimal in terms of usability. Therefore, an in-band wireless device pairing scheme providing high security while maintaining good usability (simple pairing process and user interaction) is highly desired. In this work, we propose an easy-to-use mutual authentication device pairing scheme, named Swipe2Pair, based on location proximity of pairing devices and wireless transmission power randomization. We conduct extensive security analysis and collect considerable experimental data under various settings in different environments. Experimental results show that Swipe2Pair achieves high security and usability. It only takes less than one second to complete the pairing process with a simple swipe of one device in front of the other.