Invoicing software for the Ghostbusters

As a final project for INST631 (Fundamentals of Human-Computer Interaction) at the University of Maryland, I designed a new technology to be used by the Ghostbusters.

I created a product called Spirit Billing—a piece of client invoicing software that integrates directly with the Ghostbusters’ ghost trap technology. Spirit Billing can be used to generate an invoice and charge a specified client for their outstanding balance based on the contents of the ghost trap. My final product helps the Ghostbusters conduct business more smoothly without modifying their existing ghost trapping protocol.



After capturing their first ghost at a fancy hotel, Peter rattles off a list of various fees owed and jots them down on a paper invoice to hand off to the client. Peter has to remove his gloves to write on the pad of paper, and viewers never actually see the Ghostbusters collect payment. It would be beneficial for the Ghostbusters to have an easy way to invoice clients and accept payment onsite at the time their services are rendered, especially since their initial loan to cover their business startup costs has such a high interest rate.

Design process

Low fidelity prototype

When starting to develop my low fidelity prototype, I first identified the precise tasks I would like the user to be able to perform. My initial list of tasks was as follows:

  • Inform the system which client the trap is currently being used to trap for
  • Ghost is lured into trap and trap closes
  • Feedback provided to the user indicating that the trap currently contains a ghost
  • System confirms presence of a spirit and generates invoice for client indicated
  • Offer opportunity for client to pay immediately

I made the following assumptions:

  • The Ghostbusters want to render services first, prior to billing the client or accepting payment
  • The Ghostbusters need a way to perform the necessary tasks without using a touchscreen (in case they are on a job and still wearing their gloves)
  • The Ghostbusters charge clients fixed costs for proton charging and spirit storage
  • Only one ghost can be contained inside each ghost trap
  • Client contact and billing information is primarily entered into the system offsite, using a computer with a full keyboard

High fidelity prototype

After testing my low fidelity prototype with two people, I identified three changes to implement in my high fidelity prototype:

  • A better way to sort through a long client list
  • A way to accommodate “unknown” or “TBD” options when selecting from the client list or a method for manually entering a new client on the fly
  • A way to immediately accept payment from a client

I created a high fidelity prototype using InVision. I also developed a protocol for usability testing my high fidelity prototype and tested it with five subjects.

After analyzing the usability testing results, I identified areas for improvement and implemented two major changes to my final prototype before conducting another round of testing with five new subjects:

  • Shortened the duration of all confirmation screens from 10s and 8s to 6s; added the option to press the select button to proceed to the next screen
  • Made the “ghost in trap” alert screen more obvious by making the ghost icon blink several times

© 2023 Kristen Marie Byers