Wade Robson -- Michael Jackson Had a Child Sex Alarm

Michael Jackson went to great lengths to avoid being caught sexually abusing children ... even installing an alarm to warn him whenever someone was approaching his bedroom -- so claims Wade Robson in his latest complaint against the singer's estate.

Robson just filed an amended complaint, claiming the alarm would go off whenever someone came within 30 feet of Jackson's room. Robson claims Jackson also hung a "Do Not Disturb" sign on his bedroom door.

As we reported, Robson has filed a claim against the MJ estate demanding damages. Robson claims Jackson sexually abused him for 7 years as a child, beginning in 1990.

The details of the abuse are redacted in the complaint, but the allegations are pretty clear -- Robson claims he and MJ frequently shared a bed, Jackson often showed him porn, he told Robson they loved each other but no one would understand and he needed to keep his mouth shut.

Interesting side note -- the lawsuit mentions the Jordan Chandler case in 1993, when Robson was called to testify before the Grand Jury. Robson -- then 11 -- refused to testify and the Judge -- Lance Ito of OJ Simpson fame charged the boy with contempt. A deal was struck and Robson testified in a private session -- not before the full Grand Jury.