Abstract: A Bluetooth-based travel time detector is designed by using serial communication and embedded technolo-gy .The device can automatically collect the Bluetooth MAC addresses and corresponding time stamps and then save the data on a local storage device .Laboratory studies are used to study the relationship between average undetected rate and vehicle speed as well as the locations of first-time monitoring sites .The detection accuracy of the device is also tested through field trips against the following factors :average speed ,detection rate and number of the paired devices .The T-test ,Mann Whitney U-test and W-W test carried out all indicate that the device is reliable for travel time detection .In ad-dition ,the shortcomings of the device and the recommended improvements are also summarized at the end of the paper , which provides basis for further research on Bluetooth detector .