Inventory is the register: each equipment record carries its identifier, category, status and last report. Live Map places the same set geographically, with filters for site, category and status so you can narrow a busy map to the equipment you need.
Last-seen matters more than it looks. A unit that has not reported for a while is not necessarily faulty: it may be parked where there is no coverage, retaining entries in its store-and-forward log, which holds 300 entries by default. Check the pattern and reporting conditions before treating it as a fault.