The 2.0 version is not well tested, there may be issues.
Check the FAQ before asking a question, it may already be answered there.

Adds an alert scanner reading missing materials for ghosts in it's logistic network.

What does it do

Factorio repeatedly scans construction requests and displays missing materials as alerts. These alerts have a lifetime of 10s and are cycled through once all requests have been scanned. This mod catches incoming alerts and stores them past their lifetime, making them available to the circuit network via a combinator. This enables accurately reading more than the 601 visible requests but may cause delays in the detection of additions and removals.

Features

The mod supports scanning of entity ghosts, tile ghosts, cliffs, and upgrades. It should support any modded entities that do not mess with ghost prototypes. Unsupported entities are noted in the log and ignored.
This mod is compatible with multiple surfaces and forces, although forces are largely untested.
There is no limit on the number of materials that will be scanned, but the scan time increases linearly with the number of entities.

About Performance

This mod is inspired by Optera's Ghost Scanner, which has major performance issues. So the main target was good performance, no lag spikes and scalability.

Most of the processing time (>50%) is taken by retrieving the active alerts (player.get_alerts), which is proportional to the number of alerts displayed to the player. In order to minimise the impact, the mod offers a setting to reduce the number of displayed alerts. It is recommended to set this to the minimum of 2 if you experience reduced ups.

The other factor is the number of active scanners, i.e. those outputting signals. It should therefore be avoided to have multiple scanners in the same network, as they generate the same output anyway. Scanners in inactive networks like mining outposts should only add minimal performance cost.