I redesigned a security system control to bring delight and ease to frequent users while still alarming intruders.

  • individual project
  • context: Introduction to Interaction Design, Spring 2016, four weeks
  • deliverables: concept video, physical prototype, code, documentation
  • role: concept generation, concept video, code (Processing), physical prototyping (foamcore), photography

Project Description

A typical security system for a home, office, or other building can create a lot of stress due to the grating alarm sound, especially when you can’t remember the four-digit code. This is understandable given the rare case that it is an intruder breaking in, but what about the people who belong in the area? Especially for frequent users, how could an alarm system be designed to relieve their stress but still maintain its functionality as a warning for intruders?

I wanted to design a control that would use a similar conceptual model to the current method of disarming security systems: as the user enters, the alarm tone sounds; their input is their code; their feedback is the alarm tone stopping, or persisting if they got the code wrong. I wanted to add a sense of fun and ease for the frequent user on top of that model. Inspired by the way we play musical instruments, I designed a new control that would use personalized fingerprint configurations instead of four-digit codes and would play various tones with musical considerations.

This project allowed me to get into the details of a control with a single input and resulting action. Limiting the interaction to such a small scope meant that each design decision was more carefully considered than would otherwise be possible. The focus of this project was on designing affordances, signifiers, and feedback.

How can an alarm system be designed to relieve stress but still maintain its functionality as a warning for intruders?

How It Works


As the user enters, the system is triggered. The screen on the console lights up and it begins to play the alert tone. The user presses in his or her personalized fingerprint configuration to stop the alarm, getting clear feedback that the alarm has stopped with a tone that sighs away. Arming the system is as easy as entering the fingerprint configuration and waiting for the same tone that marks the system’s recognition of the user.

The tones have been designed so that as a user becomes accustomed to them, the “sigh” of the “disarmed” tone turns into a pleasant welcome home. The alert tone remains the same, but depending on context, the perfect fifth can be either pleasant or grating. An intruder without familiarity with the tones would still be alerted, but the stress levels for a frequent user would be much lower.



Touch screens are all around us today. Most of us even choose to carry at least one around with us at all times. This multi-touch technology in our pockets can be used by this security system with the specific application of this control. Inspired by multi-touch technology and the fingerings essential to playing musical instruments, I chose to use a personalized fingerprint configuration as the input for this control.

Aural Signifier


The alarm tone I’ve chosen for this system is a perfect fifth (the first two notes of “Twinkle, Twinkle Little Star” played together). In Western music, perfect fifths can be combined with other notes and contextualized differently to change the mood of the music. The repetition of the alarm (and its jarring synthesized tone) creates a sense of urgency and stress to someone who isn’t familiar with the context of the “disarmed” tone. However, knowing the “disarmed” tone allows a frequent user to hear the fifth in context and not be as stressed.

Aural Feedback


The major triad is a simple, pleasing, and recognizable chord. It’s common to Western music and generally considered to be a “happy” chord. I chose to use this chord, played once and fading away at the end, as the “disarmed” tone — feedback for a successful input. Following the same design principle of minimalist yet aesthetically pleasing design, the major triad with a “sighing” feeling is both simple and calming.

If the input is unsuccesful, a broken fifth will provide aural feedback. It uses the same notes as the perfect fifth but instead of playing them together, plays them alternately.

Physical Prototype


With 1/4” white foam core, I built a casing for an iPad Air based on the security system consoles in the rooms at Carnegie Mellon’s School of Design. The first version was a simple cutout I placed over the screen, but it evolved into a full slipcase with buttons and emulated speaker holes.

Coded Prototype


The screen lights up on approach or as the system detects a key in the lock. A subtle on-screen grid hints at coordinates and locations. Even though the security system is not reliant on or expectant of a precise positioning, the grid can visually help the user remember what they’re doing. As the screen senses the user's fingerprints, small off-white circles make the print arrangement visible so he or she knows the input has been registered. When the system recognizes the configuration, the circles will fade away with the sound and the screen light. In the case that a configuration is entered that it doesn’t recognize, the circles will jiggle, letting the user know that it registered an input but it didn’t seem to match a recognized configuration.

I used Quappi’s app called Processing iCompilers for iOS to build a semi-functional digital prototype of my proposed alarm system. This allowed me to create a prototype that would utilize the multi-touch technology to recognize a set of fingerprints and visualize them, helping me more carefully design the visual interface of my control.

"Fingerprints" fade away as visual feedback