We broke the story ... Riggle's wife, Tiffany, filed for divorce in October after 21 years of marriage, but Rob claims things got worse shortly after when $28,000 in emergency money went missing from his home office ... and he began to feel as if he was being watched.

According to the docs ... Riggle was staying at their smaller home, while Tiffany stayed with their 2 kids at the family home. He says he confronted Tiffany about the $28k because she had access to his pad, but she denied knowing anything about it.

Around the same time, Riggle alleges Tiffany hacked into his Apple account and downloaded his emails, texts, contacts and photos ... but then he says things got really strange.

Riggle claims Tiffany somehow had knowledge of private conversations he'd had in his home office either with or about his girlfriend and assistant, and she -- or other anonymous sources -- would text or email them referencing the private info.

Because of these alleged leaks, Riggle says he and his girlfriend formed a misinformation scheme, planting false info to test whether any of it later leaked out ... and sure enough, he claims his suspicions were confirmed.

So, according to the docs, Riggle had his home electronically swept for devices in April ... and claims a hidden spy camera was found in his smoke detector.

He says the device had a memory card with more than 10,000 videos with sound on it, and he believes it was installed in August 2020 and possibly monitored him until he discovered it.

And, get this -- Riggle claims one of the vids shows Tiffany standing on a ladder installing the spy camera, and another vid shows her sitting on the floor of his home office counting money ... which Rob believes is the $28k he says went missing.