A phone no longer shows its factory hardware ID to every Wi-Fi network. iPhones have used a private MAC address per network by default since iOS 14, Android since Android 10, and Windows offers it as an option. The address is invented per network, so tracking a device across locations is harder. It also clashes with MAC filters, parental controls and some hotel portals. This guide targets a just-changed phone that home, work or gym Wi-Fi no longer recognises. Every Wi-Fi client needs a unique MAC (Media Access Control). Apple says a constant address lets observers link a device to activity and location over time; a private one breaks that fingerprint. My view: keep it on almost always; failures usually come from network configuration, not the handset.
- Key Point: Different addresses per network make cross-location tracking harder.
- Key Point: MAC filters, parental controls, reservations and captive portals may reject an unfamiliar address.
- Key Point: Use a fixed private address at home; keep randomization on public Wi-Fi.
How the three systems handle it
The principle is one address per network. Apple enables it by default on iPhone, iPad and Apple Watch from iOS 14, iPadOS 14 and watchOS 7, and on Mac from macOS Sequoia 15. In iOS 18, Settings > Wi-Fi and the network’s info button offer three choices: Off uses the factory MAC; Fixed keeps one private address and is default on WPA2 or better networks; Rotating changes it every two weeks and is default on open or weak networks. One detail explains “ayer funcionaba”: forgetting a network also forgets its private address unless less than 24 hours have passed; erasing content or resetting network settings makes the next connection use another address.
Android’s Open Source Project documentation says that from Android 10 a random MAC is default and can be toggled per network in Settings. The default is persistent: calculated from network name and security type, kept until a factory reset. Unlike iPhone, forgetting and re-adding a network does not change it. From Android 12, non-persistent randomization renews on connection after 24 hours, or if the router’s IP lease expired and the device was offline over four hours.
Microsoft calls it random hardware addresses. While scanning for networks, a computer emits its physical MAC, a signal shopping centres, shops or public spaces can use to follow movement. If the hardware supports it, enable it for all networks in Settings > Network & Internet > Wi-Fi, or for one under Manage known networks.
Where clashes appear
Some networks identify devices by MAC, so a new address looks unfamiliar.
- Router MAC filter: if a router admits only listed addresses, a private-address phone is missing. Apple advises leaving it off: it does not stop interception, MACs can be copied or spoofed, and some devices vary by network; a WPA2 or WPA3 password protects the network, not the list.
- Company and school networks: Apple has a document for administrators who control MAC access. On networks known before an update, a rejected private address makes the device try the factory one immediately. Organizations can adapt the network or disable the feature via management profiles.
- Captive portals: hotel, train and gym login screens rely on recognising a device. Android says persistent addresses help the network remember it and skip the screen; a rotating address, such as Apple’s Rotating option on open networks, makes repeat logins likely.
- Parental controls and router reservations: Android cites parental control as a feature that depends on a stable MAC. If a child’s phone was limited by address, the rule may stop applying.
- “dispositivo nuevo” alerts: routers and carriers may warn on the first connection with a private address; Apple says it is not necessarily an intruder. Before disabling anything, Apple advises installing updates and retrying. For general Wi-Fi trouble, diagnose slow Wi-Fi without blaming the operator.
When disabling makes sense
On a home network you control, disabling it for one device is reasonable when the router must always recognise it. iPhone’s Fixed option often suffices: default on WPA2, stable and recognised; Android’s persistent mode is similar. Add that private address to the router rule instead of reverting to the factory MAC.
Public networks are the opposite: leave randomization on. An airport or shopping-centre network need not know a phone belongs to yesterday’s visitor. These failures reveal designs from another era. MAC filtering was weak; randomization mainly creates support tickets. When a phone cannot join, ask why the network relies on an identifier that can be copied, spoofed or changed.
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