Device coverage explained

The number on the sales page is the least informative part of a subscription. The counting rule, the reassignment rule and the per-platform feature list decide whether it fits your household.

What a device slot actually is

A device licence is permission to have the product installed and active on one device at a time. A five-device subscription is five of those permissions, held in the vendor's account system and consumed as you install. The word "device" is doing a great deal of work in that sentence, and vendors define it differently.

Three things are worth separating, because product pages tend to merge them:

The count: How many simultaneous installations the subscription permits.
The counting rule: What consumes a slot. On most subscriptions a phone consumes the same slot as a desktop computer; on some, mobile installations are treated separately or are unlimited.
The reassignment rule: Whether a slot can be freed when a device is replaced, sold or lost, and whether that is done from the account or requires contacting support.

The count is on the sales page. The other two are in the subscription terms or the support documentation, and they are the ones that determine whether the subscription fits a real household.

The three counting models

How subscriptions are commonly structured, and what to verify for each
Model	How it works	What to verify
Fixed device count	A set number of simultaneous installations across any supported platform	Whether mobile devices consume slots, and how a slot is released
Platform-specific	Separate allowances, or separate products, for desktop and mobile	Which platforms are included at all, and whether mobile is a separate purchase
Household or unlimited	Coverage described by household rather than by a number	How the vendor defines a household, and any fair-use limit in the terms

"Unlimited" in particular is a term the vendor defines for itself. Where a subscription uses it, the definition and any fair-use provision will be in the terms, and reading that clause takes less time than discovering its meaning at installation number nine.

Why platforms are not equivalent

The same subscription behaves differently on different operating systems, and this is not a matter of vendor effort. The platforms permit different things.

Windows

The most permissive of the desktop platforms for security software, and the one where suites offer the fullest feature set: on-access scanning, a firewall layer, ransomware protection, web filtering. It is also where a product coexists with Microsoft Defender Antivirus, which steps aside when another real-time product registers itself.

macOS

Third-party security software runs with fewer privileges than on Windows and typically needs explicit permission — full disk access, a system extension approval — granted by the user after installation. Apple's platform security documentation describes the built-in protections that are present regardless.

Linux

Consumer security suites frequently do not cover desktop Linux at all, and where they do the build is usually narrower. A subscription advertised for "desktop" is not by itself a statement that Linux is included; the system requirements page is.

Android

Applications are isolated from each other, so a security app inspects what the platform allows it to inspect: applications being installed, files in shared storage, and network or web activity through the permissions it is granted. Google Play Protect is present on certified devices as a baseline.

iOS and iPadOS

The strictest of the five. Applications cannot scan other applications or the system, so a security app on iOS is generally a combination of web filtering, a VPN, breach notification and similar services rather than a scanner. That is a platform constraint, not a shortcoming of any particular product, and it is the reason comparing "does it support iOS" is less useful than comparing what the iOS version actually does.

The practical consequence

Compare per platform, not per subscription. A licence that covers six devices is not six equivalent installations if four of them are phones running a fundamentally different build. Check the feature list for each platform you intend to use before deciding the count is the important number.

A worked example: seven devices

Take a household with two adults and two teenagers: two Windows laptops, one MacBook used for study, three phones (two Android, one iPhone) and an iPad. That is seven devices under the usual counting rule.

List them by platform, not by person. Three desktop installations, three mobile, one tablet. The platform mix determines what each installation can do.
Decide which ones need a paid installation at all. The iPad and the iPhone will receive web filtering and account monitoring rather than scanning. That may be worth a slot or it may not, depending on whether those features are wanted.
Check the counting rule against the list. A five-device subscription covers this household only if mobile devices are treated separately or if two devices are left out.
Check the geography clause. A student moving into a share house is still in the household by most definitions, but "household" is defined in the terms and some definitions are about the residence rather than the family.
Leave one slot spare if the budget allows. Devices get replaced mid-term, and a spare slot avoids needing the reassignment process at an inconvenient moment.

Replacing, selling and losing devices

Slots are consumed at installation and released by the account, not by the device disappearing. Three situations come up regularly.

Replacing a device. Uninstall the product from the old one before disposing of it, then check the account console to confirm the slot shows as free. Uninstalling without checking is how households arrive at an allowance that is full of devices they no longer own.
Selling or giving away a device. Remove the product and sign out of the vendor account on that device. A factory reset removes the software but does not necessarily release the slot in the vendor's records.
A lost or stolen device. Release the slot from the account console. If the product includes a remote lock or locate feature, that is a separate function with its own requirements, and it only works while the device is powered and connected.

If a device cannot be released from the console — because it is gone and never signed in again — the vendor's support channel handles it. That is one of the practical reasons the support question appears on the comparison list.

What happens to the count at renewal

A subscription renews at the tier you bought, for the device count you bought, at the renewal price in the terms. Households change more often than subscriptions do, so the renewal date is a sensible annual checkpoint: count the devices actually in use, remove installations on devices that have left, and decide whether the tier still matches. Changing tier is usually easier before a renewal processes than after.

The related billing points — where the renewal price is published, how far ahead cancellation must be done, and what the ACCC says about consumer guarantees — are covered on the choosing software page.

The short version

Quick answer

The device number on the sales page is the least informative part of the offer. What matters is the counting rule, the reassignment rule and what the product actually does on each platform you intend to install it on. All three are documented on the vendor's own site, and all three are worth reading before purchase rather than after.