HaLo: a Hand-held Localization Device Based on Nokia n900

HaLo is a hand-held device transferred from Nokia n900 smartphone for real-time localization of a suspect who is conducting crimes in a wireless crime scene. We collect only wireless signal strength information, which requires low level legal authorization. For private investigations on campus, it does not require only legal authorization. The basic idea of localization is to collect wireless signal strength samples while walking. The position where the maximum signal strength is measured will be a good estimate of the suspect device’s location. The key challenge of accurate localization via the hand-held device is that the investigator has to control its walking speed and collects enough wireless signal strength samples. We found that digital accelerator on a smartphone and GPS are very often rough for measuring walking speed. We propose the space sampling theory for effective target signal strength sampling. We validate the localization accuracy via extensive experiments.

In the following demo, we placed a laptop which was sending out ICMP packets inside one classroom, used HaLo to sniff along the corridor and finally located the laptop. Below is the story from the student conducting the experiment.

I placed a laptop in a classroom in Olsen Hall. The laptop kept sending out ICMP packets every 0.1 second. I used HaLo to locate the latop. I knew the laptop's MAC address and Channel before I conducted the localization experiment.

I started the device and launched the application in a sideway corridor. I began from one side and walked to the other side. In the HaLo system, I selected the channel that the target laptop was using, and the system returned a list of MAC addresses of devices which were active on that channel. Among these MAC addresses, I selected the MAC address of the target laptop and began to locate. I then selected ccelerometer as speed monitor.

I could see the numbers of captured packets from the screen. The signal indicator also recorded the maximum signal strength and signal strength of the current received packet. At the beginning, the signal strength was lower than -70(db), which meant the signal was weak. Then I walked along the corridor. I walked slow enough so that within each step I could collect at least one packet. As I moved forward, the signal strength was increasing. When I passed a door of one room, the signal strength reached maximum. After that, the signal became weak and I turned back when the signal
strength was below -70(db).

I came back to the position, in which I received the maximum signal strength. Because there were two rooms at that position, with one on the left side and the other on the right side. I turned around to one room first and stepped a little bit forward, the signal strength became weak. Then I faced to the other room and stepped forward, the
signal strength became stronger. I opened the door of that room and located the target.


  1. Junwei Huang, Yinjie Chen, Zhen Ling, Kyungseok Choo, Xinwen Fu, A Framework of Network Forensics and its Application of Locating Suspects in Wireless Crime Scene Investigation, in Proceedings of the 7th International Workshop on Systematic Approaches to Digital Forensic Engineering (SADFE'12), Vancouver, Canada, September 28, 2012

HaLo 1.0

HaLo 1.1 with enhanced interface

HaLo 1.2 with enhanced interface