Habit design (Hooked)
External Trigger
Outside cue prompts action
What it is
External triggers communicate the next action through information embedded in them. Four types: paid (ads), earned (PR), relationship (referrals), owned (notifications, email, app icon).
Why it works
External triggers are the entry point of Nir Eyal''s Hook Model, and their job is narrow: tell the user what to do next. Eyal sorts them by how they are acquired. Paid triggers cost money every time and cannot sustain a habit. Earned triggers — press, viral coverage — are unpredictable and unrepeatable. Relationship triggers spread through people telling other people. Owned triggers are the ones that compound, because the user has granted standing permission: an app icon on the home screen, an enabled notification, a subscribed newsletter. Only owned and earned triggers build habits, since only they can fire repeatedly at no marginal cost. The design consequence is that early paid acquisition is worth nothing unless it converts into an owned trigger before the budget stops.
How to apply it in design
The trigger must clearly transmit what to do next in the fewest words possible. Reduce ambiguity, don't shout. Owned triggers (notifications, app icons) compound over time and are the goal.
Where you'll see it
- A permission request made at the moment its value is obvious, not on first launch
- Notification copy that names the specific next action and its object
- Email subject lines that state the change, not the category
- Home-screen or bookmark prompts offered after the user has felt value
- Referral moments placed right after a success, when sharing feels natural
Example
A "your friend just joined" notification is both a clear external trigger and a social proof signal — two-stage compression.
Failure mode
Triggers that ask for vague action ("Learn more", "Check it out") fail because the next step isn't communicated. Vague triggers waste attention.
When not to use it
Do not reach for external triggers when the underlying problem is that the product has no internal trigger yet. Notifications aimed at users who never found a reason to return produce a short spike, then permission revocation and uninstalls — and permission, once refused, is very hard to recover. They are also the wrong tool for genuinely infrequent products: a tax tool or an annual insurance renewal does not need weekly presence, and manufacturing it trains the user to ignore you in the eleven months when you have nothing to say.
The ethical line
The permission the user gave is the boundary. Granting notification access for delivery updates is not consent to promotional pushes, and treating it as such is why platform-level notification trust has collapsed. Two further abuses are common: manufactured social triggers that imply a person acted when the system did — "someone viewed your profile" generated by an algorithm — and notification copy engineered to create anxiety the app then resolves. A trigger should be worth the interruption on its own terms, judged from the user''s side rather than from the retention dashboard.
What to measure
Track the share of sessions arriving from owned triggers versus paid ones over time — that ratio is the real habit signal. Alongside it, watch notification opt-out and mute rates per campaign type, which reveal the cost of each send before it shows up in churn.
Frequently asked questions
What is an external trigger in the Hook Model?
An external trigger is a cue in the user's environment that tells them what to do next, and carries the instruction inside itself. Nir Eyal classifies them as paid, earned, relationship or owned. Owned triggers — notifications, emails, app icons — are the ones that build habits, because the user has already granted permission for them to recur.
What is the difference between external and internal triggers?
External triggers come from outside the user: a notification, an ad, a friend's message. Internal triggers come from within — an emotion, a routine or a situation that makes the user reach for the product unprompted. Products begin with external triggers and succeed when use becomes attached to an internal one.
Why do vague calls to action fail?
Because a trigger's function is to transmit the next action, and 'Learn more' or 'Check it out' transmits nothing. The user has to work out what will happen if they tap, and that ambiguity is enough friction to lose them. A specific verb attached to a specific object converts substantially better.
When should an app ask for notification permission?
After the user has experienced value and at a moment where the benefit of the notification is self-evident — when they set a reminder, follow an item or complete a first task. Asking on first launch, before any value exists, is the most common way products permanently lose the only trigger channel that compounds.
Related skills
Source: Eyal — Hooked (Ch. 2)
Practise External Trigger on a real brief
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