Sandra attaches her PDA, with built-in Wi-Fi card, to the dashboard and starts the Sound Pryer application for an alluring music experience. As she hits the road, Sound Pryer plays her favourite music on the car stereo. After a while she is bored by driving. Suddenly, the icon of a red lorry appears on the screen. She says to herself: “It must be that one over there”, as the latest Cardigans song fills her loudspeakers. Sound Pryer returns to playing her own music after she passes the lorry and sees it fall behind in the rear mirror. Sandra thinks “Cool guy, I have to get that music at the next stop.” We present Sound Pryer, which is an implemented peer-to-peer application of mobile wireless ad hoc networking for PDAs. It enables music eavesdropping in traffic encounters, by streaming MP3 files via the Real Time Protocol. The metaphor used to guide the design of Sound Pryer is that of a “collaborative” MP3 player. A user can play his or her own music, but also tune into other players and hear what they are playing as long as he or she is within close proximity. The Sound Pryer application serves pure entertainment purposes: the fun of listening to music, either one’s own selection or somebody else’s. It draws on the idea that people take an experiential and aesthetic interest in the surrounding traffic, and that they are willing to share music, since people are effectively anonymous to each other in that situation. Still the visual, and now audio, contact provides for a special and titillating shared experience, that of prying into other cars.


With a CSCW perspective the activity of sharing music is an interesting leisure activity. It is pursued in a variety of forms, from the simple ways, such as physically handing over a record to a friend, to making digitally encoded music files available to unacquainted users through large-scale Internet peer-to-peer systems. However, we are interested in the sharing experience that takes place when jointly listening to music. Is it possible to transpose this kind of sharing to the situation of brief meetings that occur among unacquainted people on the roads? Would a tool like that make road use more enjoyable?

SoundPryer is an application designed for sharing music experiences between people in vehicles in the immediate surrounding. This is accomplished by streaming MP3 files between nodes in an ad hoc network. Since the application is based on handheld computers, the usage of the tool is accommodated in a wide variety of settings.


We are currently working on a series of prototypes to collect requirements, as well as evaluating the concept of sharing music in traffic. We have completed two protypes. The first is a preliminary version of the full concept running for the Pocket PC/Pocket PC 2002 OS. This version has been tried successfully on the Compaq Ipaq 3850 and the Compaq Ipaq 3760 both running Pocket PC 2002 and making use of the Lucent Orinoco (Silver) WLAN card (and the WLLUC461 driver).

The seconds prototype was used in Wizard of Oz experimental evaluation to refine our GUI approach. The test comprised two handhelds, a remote control and the Sound Pryer dummy faking a full implementation. See the evaluation for further information on how the test was performed.

Download source code [zip] 34105 KB


In order to deepen our understanding of the SoundPryer concept in the traffic context and refine the requirements we ran a test. Our goal was to get an idea of the prototypes ability to provide awareness of from whom you are receiving music. Does the user make a connection of events in traffic and the corresponding icons etc. in the interface?

We used a “Wizard of Oz” evaluation method consisting of two handheld computers connected via a WLAN. The first was mounted in the vehicle next to the driver and ran a limited implementation of the SoundPryer concept. It only displayed awareness information and played local files – this prototype was not able to receive and play streams. We prepared it with a selection of snippets of music files. The “wizard” controlled the other device. It worked as a remote control from where it was possible to send commands to first handheld, e.g. making it show a red car and play the fifth track in the playlist. The user was instructed to drive along a particular route and interact with the prototype when the situation allowed. The wizard looked out for vehicles along the road and sent commands that made the first prototype show a corresponding representation of that vehicle. The Wizard also governed the playback to reflect the situation at hand. Thus, we were able to obtain an illusion of the full SoundPryer concept.

We collected the following feedback by performing the test with one user:

  • Using a stylised shape and the colour of a vehicle provides a clear connection to encounters in traffic. However, low-contrast colours were hard to observe.
  • It was hard to discern details in the GUI, i.e. the title of tracks.
  • It was hard to use software buttons on the touch sensitive screen, however hardware buttons gave tactile feedback that made them easier to use.


Östergren, M. and Juhlin, O. (2008)  Sound Pryer: truly mobile joint music listening, in Creative Interactions – The MobileMusicWorkshop 2004 – 2008 (eds) Nicolaj Kirisits, Frauke Behrendt, Lalya Gaye, Atau Tanaka University for applied arts, Vienna. ISBN 978-3-200-0-1221-9.

Juhlin, O. and Östergren, M. (2006). Time to meet face-to-face and device-to-device. In Proceedings of the 8th International Conference on Human Computer Interaction with Mobile Devices and Services – Mobile HCI 2006. ACM Press, pp. 77-80
[PDF] – Short paper

Östergren, M. (2006). Traffic encounters – Drivers meeting face-to-face and peer-to-peer. PhD thesis. Studies in Applied Information Technology. IT-University of Göteborg.
[PhD thesis site]

Östergren M. and Juhlin, O. (2006). Car Drivers using Sound Pryer – Field trials on Shared Music Listening in Traffic Encounters. In (eds. O’Hara, K. and Brown, B.), Consuming Music Together: Social and Collaborative Aspects of Music Consumption, Springer, Series of Computer Supported Cooperative Work, vol 35, pp 173-190.
[PDF] – Book chapter

Östergren, M. and Juhlin, O. (2004). Sound Pryer: truly mobile joint music listening. Presented at The 1st International Workshop on Mobile Music Technology, Göteborg, Sweden.
[PDF] – Workshop paper
[PPT] – Presentation

Östergren, M. (2004). Sound Pryer: Adding Value to Traffic Encounters with Streaming Audio. In Proceedings of ICEC’2004 – the 3rd International Conference on Entertainment Computing. Springer Verlag, pp 541-552.
[PDF] – Full paper

Östergren, M. (2003). Sound Pryer Field Trials: Learning About Adding Value to Driving. Presented at the workshop Designing for ubicomp in the wild: Methods for exploring the design of mobile and ubiquitous services, at MUM’2003.
[PDF] – Workshop paper

Axelsson, F. and Östergren, M. (2002). SoundPryer: Joint Music Listening on the Road. In Adjunct proceedings of UBICOMP’02 – the 4th International Conference on Ubiquitous Computing. Springer Verlag, pp 39-40.
[PDF] – Poster

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