P6 – The Elite Four

The Elite Four (#19)
Jae (jyltwo)
Clay (cwhetung)
Jeff (jasnyder)
Michael (menewman)

Project Summary

We have developed a minimally intrusive system to ensure that users remember to bring important items with them when they leave their residences; the system also helps users locate lost tagged items, either in their room or in the world at large.


The system we will be testing is a prototype with the basic functionality described in the project summary above. The system is able to detect when a user leaves the room, alert him/her if tagged items are missing (task 1), and help him/her find the items either inside (task 2) or outside (task 3) of his/her room. For our tests, we will have our users perform each of the three primary tasks. The goal of these tests is to ensure that our prototype is an intuitive and effective system for the average user.

Implementation and Improvements

P5 Blog Post: http://blogs.princeton.edu/humancomputerinterface/2013/04/22/the-elite-four-19-p5/

We have not made any changes to our working prototype since submitting P5. However, we certainly plan on improving and adding features before the final submission, focusing on the feedback we receive from our participants.


i. Participants:

Participants were randomly selected from Terrace Club. At the time of testing (during the afternoon) students who were working in the dining room were approached and asked for their participation. Amongst the users was a senior MOL major, a senior COS major and a senior HIS major. Each of the participants were members of our target user group, as they all lived in on-campus dormitories with automatically locking doors. More specific demographic information can be found in the questionnaire data within the Appendix.

ii. Apparatus:

We conducted the tests using our prototype. The current prototype uses an Arduino Uno to control LEDs as well as our RFID receiver and transmitter. These components are connected with a breadboard and jumper wires, along with miscellaneous items like electrical tape. We conducted our tests at Terrace Club, which was not a dorm room per se but sufficed because it has doors.

iii. Tasks:

Users should be able to perform three tasks with our prototype. The first task (easy) is to identify when a door has been opened and alert the user if s/he tries to leave without tagged item(s). The second task (medium) is for the system to help the user locate lost tagged items in his/her own room. Our final task (hard) is to help the user locate lost tagged items outside of his/her room. This task is very similar to the second from the system’s point of view, but for the user it is far more difficult, since the potential location of the lost item(s) is much greater.

iv. Procedure:

We conducted the study by setting up in a semi-public area and asking random students if they would like to participate. At that point, we showed them the consent form, asked them to perform our prototype’s three tasks, and had them fill out the demographic and post-task questionnaires.

Test Measures

For task 1, we had each participant leave the room 10 times with the tagged item and 10 times without. The resulting raw data can be found in the Appendix. Our system consistently identified the item 70% of the time when the user had the tagged item. It’s important to note that the RFID transmitter was generally put in the user’s sweatshirt or pants pocket, which appeared to interfere with the signal strength. We also had User 2 experiment with the left vs. right pocket of his sweatshirt since the sensor was on his right side in our setup. In his right pocket, our system was 5 for 5, but in his left pocket, it was only 2 for 5. We also tested our system without the tagged item to test that there were no false positives. For Users 1 and 3, we varied where the tag actually was while we were testing this. Since a college dorm room isn’t very big, there were realistic scenarios where the transmitter was in a pants pocket on the floor just a few feet away from the door, and these were the situations where false positives were detected. This will be a difficult problem to solve.

For task 2 and 3, we measured the time required to find an object in each of 3 preset hidden locations. We made sure this test was double-blind by having one group member hide the transmitter and a different group member following our participant as he or she tried to locate it. Throughout all 3 of the tasks, we made sure to take note of any qualitative comments or suggestions they made.

In addition we had each participant complete a more quantitative response form. In this form they were asked to rate the intuitiveness and effectiveness of our system during each task.

Results and Discussion

Users were not satisfied with the current alert system, which just uses red and green LEDs to inform the user of tag presence. This was shown to be inadequate for all of our users, who were somewhat unaware of the LEDs’ presence for all three tasks. For the first task, users would often be past the door before they could see the LED light up, especially if they simulated the situation as if they were in a rush. For the second and third tasks, users would have to spend a lot of time looking down at the LEDs to see how quickly it was blinking, and since they were looking around at where they were going, they would sometimes miss important changes in blinking speed. As a solution to this we will be adapting our prototype to add audio notifications as well. We hope that this change will help make our system’s alerts more intuitive to the user.

There also some rather severe usability issues with the item finding feature. This feature had issues with responding quickly and accurately to distance changes. This is a result of our RFID transmitter having a weak signal and only transmitting every ~2.4 seconds. This meant that proximity updates to the user were too slow and caused confusion. In order to remedy this issue, we will be adding an antenna that will increase signal strength and reduce transmission time. This means faster updates to our user and a much more usable system.

Users were also confused by the use of LEDs while using the finding feature. In the current prototype, both red and green LEDs flash at varying rates depending on tag proximity. However, users complained that they were unsure whether the tag was just far away or fully out of range. To fix this we are now using the green LED to display proximity and the red LED to indicate that the tag is out of range. One user even suggested including more LEDs to indicate proximity. For example, it would flash red if the tag is out of range, orange if the tag is at the edge of its range, yellow if it is near the middle of its range and green if it is very close. After implementing and testing the method of using the green LED to display proximity and the red LED to indicate that the tag is out of range, we have decided that users are satisfied with this and that we do not need to add more LEDs.

Another issue users observed was that the tag was not always detected by our system when opening the door. This occurred when the tag was covered (i.e. in pants or a backpack), and is is a severe issue for us. It is caused by the weak signal strength on the transmitter, and because of this the new antenna that we will add should solve this problem as well. We will also need to decrease the threshold of signal strength where the tag is considered found, as the stronger signal from the antenna will mean the tag could be detected from further away which could create more false positives.


Consent Form:


Testing Script:


Demographic Questionnaire:


Demographic Results:


Post-Task Questionnaire:


Post-Task Results:


Task 1 Data:

With tagged item (10 times)

Without tagged item (10 times)

User 1

7 right, 3 wrong

8 right, 2 wrong

User 2

7 right, 3 wrong

10 right, 0 wrong

User 3

7 right, 3 wrong

8 right, 2 wrong

Task 2 Data:

Location 1

Location 2

Location 3

User 1

Time limit reached


Time limit reached

User 2




User 3