Rules of Play
How to Enter
Extreme Sensing

The Sixth International Conference on Information Processing in Sensor Networks (IPSN '07) IPSN '07 will be hosting an Extreme Sensing competition April 26, 2007. Each team will need to build a sensor system using five sensors or less that can count people walking through a 10ft x 10ft arena. In Phase 1, the arena will be placed in a high traffic area and all teams will sense normal foot traffic from conference attendees for a duration of 10 minutes. Points will be awarded for correct detections and subtracted for false positives and false negatives. In Phase 2, each team must try to walk through the arena 10 times without being detected by their opponents' sensors, in order to increase their own score while decreasing the scores of their opponents. Results will be broadcast live during Phase 1, providing each team an opportunity to discern ho wthe other systems work and how they might fail. For more details about the competition, and how to enter, visit the URL listed above. The grand prize will be a Nintendo Wii.

NEW! Results, pictures, and a video are now posted below.

Rules of Play

Each team must build a sensing system to count the number of people that exit from a 10ft x 10ft arena, which will be located in a high-traffic area such as a doorway. Each team must setup a sensing system around the area, leaving two sides and the center unobstructed for people to walk, as shown in the diagram below. Unobtrusive sensors such as floor sensors or ceiling arrays will be permitted in the main arena area. Teams may use passive infrared motion sensors, active infrared break beams, ultrasound, dopplar radar, floor sensors, etc. A system may also include combinations of sensors, with two restrictions: 1) no system may have wires more than 12 inches in length* 2) no system may use more than five pixels in total, eg. no cameras with more than five pixels, and no more than five single-pixel** sensors. Actuators will be permitted, as long as they do not interfere with other teams' sensors and as long as they do not help the system emulate more than five pixels (see below**).

During Phase 1, the sensing systems will count normal foot traffic from conference attendees for 10 minutes. The arena will be empty when this phase begins, and conference attendees will be free to walk through in any way that they like. Ground truth will be obtained from a series of judges who will count the number of people who exit the arena by pushing a button on a mote. During this phase, contestants will not be allowed to walk through the arena.

Phase 2 will consist of 10 rounds in which each team is allowed to walk 1 player through the arena. The goal of each team is to score points for themselves without scoring points for competing teams. Each person may walk in any manner they choose, as long as it is monotonically forward (ie. the person cannot walk back and forth inside the arena). Teams will be assigned a random order for each round. A team may opt to skip a round, in which case they may walk multiple people during subsequent rounds (possibly simultaneously).

Thinking Strategically

If there are 3 other teams, then in Phase 2 you will need to cross an arena covered by up to 15 different sensors. Unlike Mission Impossible, it is unlikely that you will get through completely undetected. Instead, you will need to choose your walking strategies carefully to avoid the teams that are most likely to beat you, given the scores after Phase 1. The counts for each team will be shown live on a video screen during Phase 1, as shown in the Figure to the right. This is an opportunity for each team to discern how the other systems work, and how they might fail. For example, radar and PIR sensors may not detect slow moving objects; infrared break beams may count multiple adjacent people as a single person; floor sensors may not detect people with long strides; even multi-sensor systems may be fooled by multiple people walking in different directions, etc. This knowledge can then be used during Phase 2 to score points for your own team but not for the other teams. No competitive strategies are off-limits, except that all players must walk monotonically forward. This means that running, jumping, etc. are acceptable, sprays that illuminate laser beams are acceptable, etc. Be sure to focus on avoiding the sensors of the team whose score is closest to yours.

How to Enter

To enter, a team must send email to Kamin Whitehouse containing the team's name, institutional affiliation, the players' names, and a rough description of the hardware to be used. Entries must be received on or before April 10, 2007. The team should expect a response with the username and password to be used on the competition day. Email should be sent to:

On Game Day, each system must immediately*** and automatically (ie. no human intervention) report scores to a scoring server. This can be done through the following XML-RPC function:

Reporting API

bool report(int detections)

This function can be used to add DETECTIONS to the total number of detections by a particular team.

This function is provided by the competition server, for which the URL will be released on Game Day. In the meantime, the source code of the server is publicly available for testing. The code includes a XML-RPC server, a graphical visualization, and sample clients written in both Python and Java. Because this is a XML-RPC server, teams may call the function from any language that provides a XML-RPC library, including C, C++, Java, Perl, and Python, among others. See this simple "How To" to learn how to use a XML-RPC client in other languages. Teams will use HTTP authentication with the username and password provided.

In the case of any dispute, decisions about scoring and eligibility will be made by judges on Game Day and will be final. Contestants who would like to do something that might be the cause of dispute should ask for clarification of the rules and/or pre-approval of the hardware and techniques before the April 10 deadline. All rules of this contest are subject to clarification or change at any time.


Congratulations to the "Pixelators" from MIT who won the competition by count 203 out of 204 people with their RSSI based, single-pixel radio sensor! We had several excellent competing teams that used ultrasound sensors, infrared sensors, lasers, weights sensors, and radio signal strength sensors. Thanks to "Super Counting Bros" for the video of Phase I, and to the Pixelators for the following video of the complete competition!

The results of the three top-scoring teams are shown in the graph below and compared with the ground-truth results obtained by the judges. In Phase I, when the systems were used to measure normal foot traffic from general conference attendees, the results of all three teams were quite. In Phase II, when the teams could use adversarial strategies to trick other teams' sensors, the behavior of the three teams was quite different. The "Pixelators" score actually improved, indicating that it was difficult to defeat using adversarial techniques. Towards the end of the contest, the "Hawkers" score suddenly increased by almost 100 counts due to a single malfunctioning sensor.


* Wireless networks may be used. One long cable (e.g. a serial or USB cable) may be used to connect your sensor system to a computer.

** A single-pixel sensor can be defined in many ways. As a general guideline, a "pixel" is a sensor input that is directly mapped to exactly one sensor output, with no logic in between. In some cases, a single AND or OR gate on binary sensors may be reasonable (in order to make the sensor bigger, for example). Single-pixel sensors that emulate multi-pixel sensors through movement of the sensor, the use of moving mirrors, etc, will not be acceptable. Similarly, using actuators that help the sensor emulate a multi-pixel sensor (such as a time synchronized array of infrared transmitters) will also not be acceptable. Borderline and questionable hardware should be discussed before the April 10 deadline, and all hardware is subject to approval by the judging panel on Game Day.

*** The reports must be immediate enough for an outside observer to discern the causal relationship between the total score and what is happening in the arena.

For questions, contact Kamin Whitehouse