diff --git a/hardware/industrial/README.md b/hardware/industrial/README.md
index 4b2d411a2..bc2229e72 100644
--- a/hardware/industrial/README.md
+++ b/hardware/industrial/README.md
@@ -63,4 +63,14 @@ It is possible to lock the OTP changes to avoid them being edited again. This ca
 pi@raspberrypi:~ $ /opt/vc/bin/vcmailbox 0x00038021 8 8 0xffffffff 0xaffe0000
 ```
 
-Once locked, none of the customer OTP values can be accessed.
+Once locked, the customer OTP values can no longer be altered. Note that this locking operation is irreversible.
+
+## Making Customer OTP bits unreadable
+
+It is possible to prevent the customer OTP bits from being read at all. This can be done using a special argument with the OTP write mailbox:
+
+```
+pi@raspberrypi:~ $ /opt/vc/bin/vcmailbox 0x00038021 8 8 0xffffffff 0xaffebabe
+```
+
+ This operation is unlikely to be useful for the vast majority of users, and is irreversible.