What sort of hardware in particular? Just anything and everything? And do you mean 'impending failures' or 'currently dead hardware'?
LOL, though I suppose 'currently dead' hardware would present symptoms rather readily
but here's two suggestions, incase you aren't aware:
1 - Testing memory with Memtest86+ is not necessarily indicative of much when run occasionally and only once, but if left to run overnight or for several hours, symptoms of failing memory can be detected.
2 - To monitor hard disk drives, use the SMARTmon tools, specifically 'smartctl' which accesses/monitors/records all the SMART attributes of SMART-enabled drives. By checking it regularly, you can spot impending hard disk failure of several varieties.
3 - lm_sensors has the potential to warn of impending power supply failure and fan failure if used regularly, by watching for power drops and low voltages, erronious RPM on fans...
Is this the sort of stuff you're looking for, like for your own machine, or are you maybe trying to figure out a reliable way of diagnosing other machines which have mysterious or intermittent problems?