diff --git a/src/wormhole/_allocator.py b/src/wormhole/_allocator.py
index 040b913..b671692 100644
--- a/src/wormhole/_allocator.py
+++ b/src/wormhole/_allocator.py
@@ -10,8 +10,7 @@ from . import _interfaces
 class Allocator(object):
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def wire(self, rendezvous_connector, code):
         self._RC = _interfaces.IRendezvousConnector(rendezvous_connector)
diff --git a/src/wormhole/_boss.py b/src/wormhole/_boss.py
index a48ad11..c8a7ab0 100644
--- a/src/wormhole/_boss.py
+++ b/src/wormhole/_boss.py
@@ -38,8 +38,7 @@ class Boss(object):
     _tor_manager = attrib() # TODO: ITorManager or None
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __attrs_post_init__(self):
         self._build_workers()
@@ -92,9 +91,22 @@ class Boss(object):
                  "RC": self._RC, "L": self._L, "C": self._C,
                  "T": self._T}
         for machine in which.split():
-            def tracer(old_state, input, new_state, machine=machine):
-                print("%s.%s[%s].%s -> [%s]" % (client_name, machine,
-                                                old_state, input, new_state))
+            def tracer(old_state, input, new_state, output, machine=machine):
+                if output is None:
+                    if new_state:
+                        print("%s.%s[%s].%s -> [%s]" %
+                              (client_name, machine, old_state, input,
+                               new_state))
+                    else:
+                        # the RendezvousConnector emits message events as if
+                        # they were state transitions, except that old_state
+                        # and new_state are empty strings. "input" is one of
+                        # R.connected, R.rx(type phase+side), R.tx(type
+                        # phase), R.lost .
+                        print("%s.%s.%s" % (client_name, machine, input))
+                else:
+                    if new_state:
+                        print(" %s.%s.%s()" % (client_name, machine, output))
             names[machine].set_trace(tracer)
 
     def serialize(self):
diff --git a/src/wormhole/_code.py b/src/wormhole/_code.py
index e026460..7ff9603 100644
--- a/src/wormhole/_code.py
+++ b/src/wormhole/_code.py
@@ -13,8 +13,7 @@ def first(outputs):
 class Code(object):
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def wire(self, boss, allocator, nameplate, key, input):
         self._B = _interfaces.IBoss(boss)
diff --git a/src/wormhole/_input.py b/src/wormhole/_input.py
index 8a8da3a..dab364f 100644
--- a/src/wormhole/_input.py
+++ b/src/wormhole/_input.py
@@ -13,8 +13,7 @@ def first(outputs):
 class Input(object):
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __attrs_post_init__(self):
         self._all_nameplates = set()
diff --git a/src/wormhole/_key.py b/src/wormhole/_key.py
index 330833f..454808b 100644
--- a/src/wormhole/_key.py
+++ b/src/wormhole/_key.py
@@ -64,8 +64,7 @@ class Key(object):
     _side = attrib(validator=instance_of(type(u"")))
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def _set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __attrs_post_init__(self):
         self._SK = _SortedKey(self._appid, self._versions, self._side,
@@ -114,8 +113,7 @@ class _SortedKey(object):
     _side = attrib(validator=instance_of(type(u"")))
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def wire(self, boss, mailbox, receive):
         self._B = _interfaces.IBoss(boss)
diff --git a/src/wormhole/_lister.py b/src/wormhole/_lister.py
index a58ecf6..dfca877 100644
--- a/src/wormhole/_lister.py
+++ b/src/wormhole/_lister.py
@@ -10,8 +10,7 @@ from . import _interfaces
 class Lister(object):
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def wire(self, rendezvous_connector, input):
         self._RC = _interfaces.IRendezvousConnector(rendezvous_connector)
diff --git a/src/wormhole/_mailbox.py b/src/wormhole/_mailbox.py
index 061a39c..3c5413d 100644
--- a/src/wormhole/_mailbox.py
+++ b/src/wormhole/_mailbox.py
@@ -10,8 +10,7 @@ from . import _interfaces
 class Mailbox(object):
     _side = attrib(validator=instance_of(type(u"")))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __attrs_post_init__(self):
         self._mailbox = None
diff --git a/src/wormhole/_nameplate.py b/src/wormhole/_nameplate.py
index 599573b..00f2f7e 100644
--- a/src/wormhole/_nameplate.py
+++ b/src/wormhole/_nameplate.py
@@ -7,8 +7,7 @@ from ._wordlist import PGPWordList
 @implementer(_interfaces.INameplate)
 class Nameplate(object):
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __init__(self):
         self._nameplate = None
diff --git a/src/wormhole/_order.py b/src/wormhole/_order.py
index 81cb088..26671a1 100644
--- a/src/wormhole/_order.py
+++ b/src/wormhole/_order.py
@@ -11,8 +11,7 @@ class Order(object):
     _side = attrib(validator=instance_of(type(u"")))
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __attrs_post_init__(self):
         self._key = None
diff --git a/src/wormhole/_receive.py b/src/wormhole/_receive.py
index 389c0f4..7a78518 100644
--- a/src/wormhole/_receive.py
+++ b/src/wormhole/_receive.py
@@ -12,8 +12,7 @@ class Receive(object):
     _side = attrib(validator=instance_of(type(u"")))
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __attrs_post_init__(self):
         self._key = None
diff --git a/src/wormhole/_rendezvous.py b/src/wormhole/_rendezvous.py
index 9af0edb..c4e5c45 100644
--- a/src/wormhole/_rendezvous.py
+++ b/src/wormhole/_rendezvous.py
@@ -86,7 +86,7 @@ class RendezvousConnector(object):
         self._trace = f
     def _debug(self, what):
         if self._trace:
-            self._trace(old_state="", input=what, new_state="")
+            self._trace(old_state="", input=what, new_state="", output=None)
 
     def _make_endpoint(self, hostname, port):
         if self._tor_manager:
diff --git a/src/wormhole/_send.py b/src/wormhole/_send.py
index ccd4699..3c8c722 100644
--- a/src/wormhole/_send.py
+++ b/src/wormhole/_send.py
@@ -12,8 +12,7 @@ class Send(object):
     _side = attrib(validator=instance_of(type(u"")))
     _timing = attrib(validator=provides(_interfaces.ITiming))
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __attrs_post_init__(self):
         self._queue = []
diff --git a/src/wormhole/_terminator.py b/src/wormhole/_terminator.py
index 1468c07..3a14042 100644
--- a/src/wormhole/_terminator.py
+++ b/src/wormhole/_terminator.py
@@ -6,8 +6,7 @@ from . import _interfaces
 @implementer(_interfaces.ITerminator)
 class Terminator(object):
     m = MethodicalMachine()
-    @m.setTrace()
-    def set_trace(): pass # pragma: no cover
+    set_trace = m.setTrace
 
     def __init__(self):
         self._mood = None