Some wireless devices don't get detected sometimes

I have a new licenced WiFi Guard installation running on a Win10 PC and I am getting some peculiar results, mainly with WiFi connections. If I perform a scan I only see five cabled devices.

However, if I view All Devices I see 12 devices, which is correct. Interestingly, one tablet is marked Last Seen 'Yesterday' while the other table is marked Last Seen '1 days ago'. I have performed a scan in the past and seen them, but they are not visible now. They are powered on and online.

Similarly, my Android phone and my wife's iPhone are currently not visible when I scan but they do sporadically appear and they are present under All Devices. The iPhone was Last Seen 'Today' but the Android phone was Last Seen 'Yesterday' in spite of it having been in use when I last performed a scan.

Could you explain what is going on please and is there perhaps something I don't understand here?

Thank you in advance!
Regards, Andy.

My T30s Android tablet has now become visible in the scan.

This situation is not unusual. Phones and tablets often behave differently to cabled devices when it comes to responding to scans.

Why they don't always reply:

• Power-saving mode: When the screen is off or the device is idle, its WiFi chipset usually goes into a deep sleep. In this state it won't answer ARP pings or will do so only occasionally.
• OS-level behaviour: Both Android and iOS are designed to conserve battery. They keep the WiFi session alive but stop replying to certain network probes until there is user activity or other network demand.
• Probe timing: WiFi Guard sends probes during the scan, and if the device doesn't respond within a certain time-frame, it will be marked as absent for that round.

That's why you see those devices in the All Devices list (they were successfully detected before), but a new scan may miss some of them if they don't answer in time.

When a device wakes up (for example, if its screen is on, or it is actively using data, or is receiving push notifications), it will respond correctly again and show up in the scan. Although this isn't guaranteed every time, and it may take several rounds until it gets re-detected.

That's also why your T30s tablet has reappeared in scan results. It wasn't detected earlier simply because it wasn't replying at the time. This is common with mobile devices and is the reason they can appear to be detected inconsistently compared to the always-on cabled equipment.

Most important however is that this behaviour doesn't affect security monitoring. If someone were to connect a new phone or tablet to your network, WiFi Guard would detect it immediately (provided the Instant Device Detection setting is enabled), because the device must request an IP address, and that request is always visible to WiFi Guard.