The CAR Model: It’s What Drives Habits

9 min read

The consequences of an act affect the probability of its occurring again. – B. F. Skinner

In this post, we explore how your app can program habits with the Cue-Action-Reward (CAR) Model. The CAR Model gives you a tested, practical way to design experiences and products that cause habit formation. We’ll break down each step of the model and review some common pitfalls vs. successful examples.


How to Program Habit Formation

The CAR Model. Together, the cue and action constitute the habit pairing, and the reward, induces the habit to form. The user’s habit forms when a neurological association between the specific cue and the specific action is learned through reinforcement. The more surprising the reward is, the more reinforcing it is, and the faster and more effectively the habit is formed.

A quick refresher:

A habit is the learned association of a specific cue and a specific action such that, a user automatically performs the action when they experience the cue. The brain learns which habits to build (that is, which cues to associate with which actions) based on the consequences of our experiences.  Specifically: our brain only builds habits from the unexpectedly positive consequences of our behavior.

The CAR Model combines each of those steps into a framework you can use in your app to induce habit formation. The framework prescribes thinking of the ‘flow’ of your Product or experience as having three sequential steps:

  • Cue: something the user senses in their environment that they can learn to associate with an action
  • Action: the key behavior you want a user to perform
  • Reward: a delightful UX change that is shown to the user instead of the standard neutral feedback

If the cue -> action pairing is the habit you want someone to perform, the feedback -> reward is the training that your app gives their brain to learn that habit. It’s the glue, so to speak, that holds the habit together.


C is for Cue

As introduced in chapter 1, a Cue is something experienced from our internal environment (our thoughts and feelings) or our external environment (something we sense) that causes us to take a particular action. In Behavioral Design, there are three types of Cue’s: internal, external, and synthetic.

Internal Cues: Cues in Your Head

An internal cue (sometimes called an “endogenous cue”) is something that people sense inside themselves; their internal feelings and thoughts. Internal cue can be feelings and thoughts like hunger, remembering that your favorite bakery is nearby, boredom, thinking about the taste of cinnamon, anxiety, or recalling someone you used to go out drinking with.

Unlike external cue, internal cue are “inner” events that are private to a person’s brain. They have the same power as external cues to initiate a habit,  and Behavioral Designers find some particular internal cues highly attractive to pair their Product with.

A word of caution: when a negative internal cue is paired to a behavior in your app, users may come to resent that behavior – and by extension – your app. As a Behavioral Design community, we’re seeing this happening right now with much of the cultural backlash against social media apps that have long sought to leverage negative emotions as cues for their use. Users refer to the behaviors linked to negative internal cues as “addictive”, “pointless”, or worse: “destructive.” Now, people are beginning to remove these apps and behavior from their life, and go out of their way to evangelize against these apps and how destructive they can be. This can be a toxic outcome for your Product. When you can, avoid associating your app with negative internal cues. It will backfire.

External Cues: Cues Around us

An external cue is anything that someone senses from their immediate surroundings that causes them to perform a habit. When most people think of cues, they’re really thinking of external cues. The sight of a TV remote, the sound of police sirens, or the smell of fresh baked cookies are all external cues. Anything in a person’s environment can be an external cue, and each can cue a particular behavior.

For example, when some people smell cigarette smoke, it may cue them to smoke even if they didn’t particularly want a cigarette. Here, the presence of the cue in their environment did not force or coerce them to smoke. Rather, it persuaded them to smoke. It raised the probability that they’d perform the behavior by leveraging a learned association between smelling smoke and the act of smoking a cigarette.

Synthetic Cues: Cues You Control

A synthetic cue is a cue that has been intentionally constructed by a Behavioral Designer to cue a particular action. These cues are of special interest to you and your team because, as Behavioral Designers, you control them. That said, you cannot treat synthetic cues created by another Behavioral Designer like synthetic cues because you can’t control them (the other Designer does): to you and your app, they’re just external cues in your user’s environment.

For example, the particular branded color red on a Coke machine, the ‘M’ of McDonalds, or the distinctive smell of Cinnabon are synthetic cues by the Design Teams that control them. Each of these were intentionally designed and paired to specific consumption actions.

Push Notifications

The dramatic increase in smartphone usage and the omnipresence of mobile technology provides Behavioral Designers with a new powerful set of tools for designing and implementing synthetic cues for their users. Our always-on mobile devices and push notifications are a powerful way to remotely (and dynamically) present synthetic cues to users to prompt them to perform certain actions.

Notifications are easy to send: the hard part is sending the right ones at the right time. If you send a user a notification, and they don’t perform the target behavior, the neurological linkage between the cue and the action actively becomes weaker.

Through our experiences, we’ve learned that there are three main reasons certain Synthetic cues fail: (1) the user doesn’t understand what they’re supposed to do when presented with the cue, (2) they don’t have the ability to do what they are supposed to do, or (3) they aren’t motivated to do the behavior.

If you can discover why someone didn’t respond to a synthetic cue, you can change the cue to be more effective. That’s the biggest strength of a synthetic cue; you can change it!


A is for Action

The action is the specific behavior you want someone to perform more often. It’s what people will do automatically when they experience your synthetic cue.

Dr. BJ Fogg of Stanford University’s Persuasion Lab, one of the leading academic voices in Behavioral Design, promotes a model of understanding whether or not a user will act. His MAT Model Dr. Fogg’s MAT Model suggests that users perform a habit when they have adequate Motivation, Ability, and in the presence of a Synthetic Trigger.

As a Behavioral Designer, you need to balance how motivated a user is against how difficult a task is. If an action is too hard, the user won’t do it. If the action is too easy, then you’ve wasted the user’s motivational potential. They were ready to do something hard, but you didn’t ask enough from them. Ideally, your product should present a synthetic cue for an action that someone is able to perform when they’re motivated to act.

Some Actions are easier to turn into user habits than others. When we at Boundless Mind help our clients identify what actions inside their app would be best to turn into a habit, we use the following criteria:


Small Actions are better than large Actions

Favor a short action that can be quickly accomplished over something that takes a lot of time, rigour, focus, energy, or other scarce resources. The user is almost always busy. They have time for your app – and your habit – so long as it could already fit into their life.


Specific Actions are better than general, larger behaviors

“Walk for 10 minutes” is a more specific action than “move more”. Maybe this past New Years you heard someone resolve to “get in shape” with no more specific plan than that? People often have a hard time building habits out of general goals like “get in shape”, but “go to the gym before work on Tuesdays and Thursdays” is just specific enough to develop a mental association – a habit. When identifying which actions in your app you want to turn into a user habit, favor specific, well-described actions over abstract, nebulous, or open-ended actions.


Make sure the person is capable of actually doing the action

Favor actions that you’re certain the user is capable of performing. A good understanding of your target users will guide you towards the actions that are reasonable to ask for and help you avoid those which might be too difficult or too intense.


Pick actions that are good for people. Period.

Pick actions that align well with a person’s personal aspirations, goals, and definition of a life truly well-lived. They’re entrusting their mind to you. As an app publisher, and one equipped with Behavioral Design, you’re the closest our world has to a wizard. Use your power for good. Period. Failure to do so not only builds a world worse off for all of us, it will hurt your business in the long-run. `

Recently, Behavioral Design and Persuasive AI have received increasing public scrutiny. This increased transparency about these techniques means users are increasingly well-equipped to expose apps using these techniques for nefarious or otherwise self-serving purposes poorly aligned with their users’ needs. They’ll call you out. If there are any doubts in your head about whether or not your app’s actions are actually good for people, we advise two starting points: Nicomachean Ethics\cite{nethics} for the ethics gut-check, and Gates Notes\cite{gnotes}\sidenote{\href{}{\textit{Gates Notes} has an expansive perspective on the problems worth solving for a checklist of the outstanding challenges to human flourishing that still need to be passionately addressed. Go build a solution for one of them. Please.


F is for Feedback

When an app’s UX responds to our actions, it’s providing us Feedback about our actions. This feedback is critical for both usability and making your app habit-forming!

It’s essential that users are always provided some sort of neutral feedback after an action is completed. It’s a signal that users’ brains need to understand that they’ve performed the correct action, and that your app detected they did it.

Importantly, feedback is deliberately separated from Reward. This is important because habits are best-formed when a user is given feedback every single time they do the correct habit action, but they’re only rewarded for it sometimes (more on why this is true in Chapter 3.)

Our brains need feedback about our actions to determine if we’ve done the action we intended and that the action had the outcome we expected. In real-life, this happens so normally that we don’t really think about it: you press the accelerator, and your car moves. You eat food, and can feel it in your mouth, and then see an empty plate. Every app interface you’ve ever used constantly provides you with feedback. Buttons click when you tap them to signal that the app received your interaction. Screens progress as you navigate through a normal usage flow. In each of these examples, you receive a GO signal to continue using the app based on the app responding to your interactions: based on the feedback it provides. (Also consider how jarring it is when your phone freezes mid-interaction!) Feedback about our behavior is how our brains know to continue behaving. And sometimes – when the feedback is unexpectedly delightful – it’s how our brains learn what to do more often in the future.

If the cue -> action pairing constitute the “What” of the habit, the feedback: reward pairing are the “How” of the habit. They’re the signals our brains need to compute the consequences of our actions, and what should happen next and more often.


R is for Reward

When the feedback we receive as the consequence of our actions is unexpectedly delightful (ie: not only was it pleasant; we didn’t see it coming!), we consider it rewarding. The brain’s Habit System activates and we become more likely to perform that action again in the future. The surprising and delightful reward we received for our behavior reinforces that cue -> action pairing, and increases our chances of doing it again: it’s the glue that locks the new habit in your mind.

When our actions have unexpectedly positive consequences, specific brain regions and the Ventral Tegmental Area becomes active and release the neurotransmitter dopamine into our Habit System. The dopamine molecule causes neuron-to-neuron connections in our Habit System to associate the particular cue we experienced with the action we just performed. In this sense, the dopamine molecule is responsible for two things: putting a smile on the user’s face, and inducing them to be more likely to do that behavior again.

Any time you’ve cracked a smile in response to something delightful and surprising that’s happened on your phone? That’s dopamine.

Feels great, doesn’t it?

Behind the smile and under the neurological hood, the dopamine molecule is actively strengthening the connections between the neurons that detected the cue, and the neurons that activate and cause a user to perform the action that yielded an unexpectedly awesome outcome to happen.


Become an Expert: Hacking Habits

Through our work at Boundless Mind, we’ve learned a lot about how Product Teams think about habits and behavior change. There are big misconceptions we often hear, so here’s what you can get right:


Truth: Our brains only build habits from positive consequences. Our brains keep a record of our experiences: memory. And habits are a form of memory: they’re a record of what’s happened to us previously to help us determine what actions we should do more often in the future.

Certainly, the brain has systems for understanding punishment. And certain types of punishments can change behavior really fast. But when we look inside the Habit System’s neural wiring, we find that it contains many more direct connections from brain regions responsible for recognizing the positive consequences of our actions, than from regions detecting negative consequences.

By and large, the brain is not wired to associate punishments with long-term behavior change and habits. This is part of why parenting techniques focused on punishment often fail to raise good-natured kids. It’s why incarceration alone often fails to change people’s habits (but rehabilitation and therapy does), and why shame or punishment for people suffering from addiction is ineffective at breaking addiction. The brain just isn’t wired for negativity to impact our habits.

It is, however, strongly wired for positive consequences – for reward – to shape us.


Truth: The positive consequences have to be unpredictable.

The brain’s dopamine-producing neurons become active and release dopamine into the habit system when we experience something unexpectedly pleasant. Pleasant alone doesn’t cut it: the system only becomes active when it’s both pleasant and surprising. The brain regions that create dopamine and connect to our habit system only become active when we experience a positive consequence when we did not expect to.

While many have an intuition that positivity is what shapes our behavior, what many misunderstand is that it is the unpredictability of the positivity that actually activates the brain’s behavior change machinery – not just the positivity alone. In this sense, our job as Behavioral Designers is to optimize for unpredictability, not just maximum positivity.


Truth: Unpredictability is mostly about pattern.

The brain’s predictions about how good the consequence of a behavior will be are less about what the positive consequence will be, and more about when the positive consequence happens. Will it happen this time? Next time? Next week? When am I going to get it next?! That’s what the brain’s trying to solve, and that’s what activates dopamine to be released into the Habit System.

Carefully controlling the pattern of consequences over time (ie: the pattern of when they are neutral vs. when they are positive) is the most effective intervention a Behavioral Designer can make to inducing a habit. This was one of the key insights of pioneering Behavioralist Dr. BF Skinner: the schedule (pattern over time) of positive consequences controls the future frequency of a behavior.

Lindsey Meredith

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