To play Guided by Voices the user first puts on the headphones and the wearable. The player then enters the game space, which is simply an area where the RF beacons have been set up (convention hall, gallery, computer lab, etc.). For this particular game we used 10 beacons creating 9 different locations in the augmented reality. There is also one beacon that the player passes as he/she enters the space that triggers a sound clip of the game narrator. This clip explains to the player the backstory of the game and how to play. The player is told that he/she is about to embark on a quest to rescue his/her elfin friend who was kidnapped by an evil wizard. The narrator goes on to explain that the player will be exploring a medieval fantasy landscape and will encounter both friends and foes as he/she travels through this world. Along the way he/she will find virtual items that will help to battle enemies and release the imprisoned elf friend. The narrator explains that to play the game, the user must simply walk through the gamespace, visiting the sites of RF beacons that are also marked in the real world by small props that hint at what will be encountered at that site.
Figure:
State diagram for Guided by Voices. Each box represents a beacon
in the environment. The text indicates the sounds played and how the
state of the augmented reality is used and updated.
As the player enters a new site the wearable receives the unique ID from
the beacon in that location and updates its internal position
information. The current game state, location information and rule of
the game are then used
to select and play the appropriate sound clips and in turn update the
game state.
For example, the player starts the game with no items. If
he/she walks over to the beacon marked by a stuffed rat, he/she will
hear a narrative sound clip that indicates that he/she has encountered
a rat and has picked it up and has placed it in his/her
inventory. Later on, if the player walks over to the beacon
representing a knight one of two narrative sound clips will play. If
the player has previously procured the rat
the narrative will play out such that the player slays the knight and
steals his sword. The player can then continue his/her quest having
successfully defeated a enemy and having won another item vital to the
completion of the total quest. However, if the player has not procured
the rat the narrative will play out such that the knight defeats the
player. The narrator then explains to the player that he/she must
start the quest again. In another instance the player may find the
beacon that represents the cage where his/her friend is imprisoned,
but will not be able to virtually unlock the door until he/she has
procured the magic spellbook from another site. The state diagram
(Figure 
) shows all the beacons that are present in
the Guided by Voices game space. Below each space is the logic that
controls the sound clips that will be played and how the game state will
be effected when a player comes within range of the beacon. There is
more than one winning path through the set of beacons, ranging from a
path that consists of visiting only three beacons to one that
visits all nine beacons.
One interaction problem that exists in the current implementation of Guided by Voices results from the range of the RF transmitters used at each site. These transmitters have a wide range compared to the small props at each location and the boundary of the transmitter is not apparent to the user. Therefore, it is not clear to users when they will be in range to trigger the sounds for a particular site. This can result in users inadvertently entering sites they had intended to avoid. One way to fix this problem would be to modify the transmitters to have a much smaller range so that the site is not entered until the user is right next to the beacon and prop. However this would require developing a new radio transmitter instead of using a commercially available one. Another solution that would also result in richer game play would be to incorporate time into the system. Currently the game state is updated once the player enters a new space and accordingly sounds are played immediately. The game could be redesigned so that the player is first informed that they have entered a new space. The player could then choose to leave with nothing happening, or he/she could stay triggering the system to update the game state and play the sounds for that location. For example, if the player entered the site that contained the dragon narrative, he/she would first hear the heavy breathing of the dragon and the cave ambiance. If the player remained in the range of the beacon he/she would wake up the dragon and end up fighting it. However, if the player quickly retreated from this location the narrative would stop and the player would have avoided the encounter with the dragon.