diff --git a/README.md b/README.md
index adf0e6c..74fa879 100644
--- a/README.md
+++ b/README.md
@@ -137,7 +137,8 @@ whether the handshake may answer status 2 ("code ignored"; one reference accepts
 source accepts it); the first frame id; and the maximum frame size. Two further things
 are worth a look on a board even though the mock's header does not flag them: the calibration memory layout and
 its coefficient type, and the status word's bits, in particular whether the "scan running" bit stays set while the
-board waits for a trigger (the source restarts a scan that reads as stopped when auto-restart is on). The DIFF input
+board waits for a trigger (with auto-restart on, the source restarts a scan that reads as stopped only when no
+trigger is configured, so as not to reset the wait for the edge; this is unverified on hardware). The DIFF input
 numbering (channel + 8) and the filler byte after scan start are agreed by both references. The scan overrun count
 is approximate: the board does not say how many scans it dropped, so the frame after a restart reports one lost.
 Errors (no device, a rejected connection code, a timeout, the scan socket closing) are written to stderr as
diff --git a/docs/claude/architecture.md b/docs/claude/architecture.md
index 2106f7c..297f01b 100644
--- a/docs/claude/architecture.md
+++ b/docs/claude/architecture.md
@@ -48,7 +48,7 @@ What feeds `Acquisition` is a `DataSource`, one of the registered *kinds*.
   `e1608_source` is the `DataSource`; `e1608_kind` and `e1608_panels` are the UI. A change to the wire
   never reaches the UI files.
 - The E-1608 source runs **everything inside `poll()`** on the producer thread: posted commands, the
-  connect state machine (Down, Scanning, Halted), the scan read, the 500 ms status check, the digital
+  connect state machine (Down, Scanning, Halted), the scan read, the 500 ms status check (its not-running restart is skipped when a hardware trigger is configured), the digital
   input/counter poll and the 20 ms waveform tick. There is no second thread. A connect attempt (discovery,
   handshake, calibration read, scan start) can block `poll()` for as long as the command timeout allows each
   step; that delays only the command queue. Every exception is caught inside `poll()`: an escape would end
diff --git a/src/source/e1608/e1608_source.cpp b/src/source/e1608/e1608_source.cpp
index 2a42cdd..81f5565 100644
--- a/src/source/e1608/e1608_source.cpp
+++ b/src/source/e1608/e1608_source.cpp
@@ -186,6 +186,7 @@ void E1608Source::open(SourceSink& sink) {
 
 void E1608Source::close() {
   if (state_ == State::Scanning) dev_.scan_stop();
+  scan_started_ = false;
   link_.close();
   connected_.store(false, std::memory_order_relaxed);
 }
@@ -212,6 +213,15 @@ void E1608Source::note(const std::string& msg) {
 }
 
 void E1608Source::fail(const std::string& msg, bool fatal) {
+  if (scan_started_) {
+    // The scan may have started before a later connect step failed: tell the board to stop, so it
+    // is not left scanning with nobody reading. Best effort; it must never throw out of here.
+    try {
+      dev_.scan_stop();
+    } catch (...) {
+    }
+    scan_started_ = false;
+  }
   link_.close();
   const bool was_up = connected_.exchange(false, std::memory_order_relaxed);
   note(msg);
@@ -283,6 +293,7 @@ void E1608Source::connect_and_start() {
   }
 
   link_.connect(host, cfg_.port, cfg_.code, cfg_.timeout_ms);
+  scan_started_ = false;
   cal_ = Calibration{};
   if (cfg_.calibrate && !dev_.read_calibration(cal_))
     note("calibration memory refused; using nominal values");
@@ -419,13 +430,16 @@ void E1608Source::check_status() {
     sink_->on_event(SourceEvent::Error, "scan overrun; restarting");
     restart_scan();
     pending_lost_ = 1;
-  } else if (!(st & 2) && cfg_.auto_restart) {
+  } else if (!(st & 2) && cfg_.auto_restart && cfg_.trigger == Trigger::None) {
+    // With a hardware trigger the board may report "not running" while it waits for the edge;
+    // restarting then would reset the wait forever, so only the overrun bit restarts the scan.
     restart_scan();
   }
 }
 
 void E1608Source::restart_scan() {
   dev_.scan_stop();
+  scan_started_ = false;
   pending_.clear();
   for (auto& r : ready_) r.clear();
   start_scan();
@@ -437,6 +451,7 @@ void E1608Source::start_scan() {
     throw LinkError(LinkError::Kind::Command, "the aggregate rate exceeds 250 kS/s");
   try {
     dev_.scan_start(queue_, cfg_.aggregate(), cfg_.ext_clock, cfg_.trigger);
+    scan_started_ = true;
   } catch (...) {
     // The board may have accepted the start (0x11) before a later step failed (the filler byte):
     // tell it to stop, so it is not left scanning with nobody reading.
@@ -444,6 +459,7 @@ void E1608Source::start_scan() {
       dev_.scan_stop();
     } catch (...) {
     }
+    scan_started_ = false;
     throw;
   }
 }
diff --git a/src/source/e1608/e1608_source.hpp b/src/source/e1608/e1608_source.hpp
index a25ab60..81bb1e7 100644
--- a/src/source/e1608/e1608_source.hpp
+++ b/src/source/e1608/e1608_source.hpp
@@ -124,6 +124,7 @@ class E1608Source final : public DataSource {
   E1608Settings cfg_;
   SourceSink* sink_ = nullptr;
   State state_ = State::Down;
+  bool scan_started_ = false;  ///< a scan start succeeded and no stop has followed
   Link link_;
   Device dev_{link_};
   Calibration cal_;
diff --git a/tools/mock_e1608.py b/tools/mock_e1608.py
index d63a340..c2195f9 100755
--- a/tools/mock_e1608.py
+++ b/tools/mock_e1608.py
@@ -327,7 +327,9 @@ class Board:
                 self.first_conn = time.monotonic()
         close_quietly(old)
         if first and self.args.drop_after > 0:
-            threading.Timer(self.args.drop_after, self.drop).start()
+            timer = threading.Timer(self.args.drop_after, self.drop)
+            timer.daemon = True
+            timer.start()
         try:
             while True:
                 b = conn.recv(1)