diff --git a/unlock-ben-eater-hardware/README.md b/unlock-ben-eater-hardware/README.md
index b1c8994..2259548 100644
--- a/unlock-ben-eater-hardware/README.md
+++ b/unlock-ben-eater-hardware/README.md
@@ -6,3 +6,6 @@ different shift register chips and different pin assignments.
 To meet the timing requirements of the SDP unlock, this code uses direct port writes
 to set and read values on the data bus.  It will work Arduino Uno and Nano hardware,
 but would require changes for other platforms.
+
+**NOTE** that this sketch **will not** work on TommyPROM hardware.  It is included here
+to help people using that hardware to unlock their chips.