We did an alarm in a shop that had been a jewellers in the 1970s and then an estate agents ever since. Unbelievably, the stairs to the 2nd and 3rd floors were lightly boarded up and had never been visited in years! Sadly nothing of value but a nearly fully kitted 1960s workshop complete with Bakelite Lucas batteries to run some sort of electric brazing iron and a retro stock room with period packaging etc... Sadly before the days of camera phones.
Found a coin (US dime) unde the floor which the householder was happy for me to keep. Later sold it for $400 on ebay US (rare mark)
Same street years later (last year in fact) found a large grotty envelope underfloor marked '2004 - £15,000 cash'... Have you seen my new motorbike?
Not really, obviously I gave it to the customer - who then confessed he'd forgotten it was there!!