diff --git a/eventlet/debug.py b/eventlet/debug.py
index cca5862..2920fd9 100644
--- a/eventlet/debug.py
+++ b/eventlet/debug.py
@@ -130,3 +130,14 @@ def tpool_exceptions(state = False):
     it normally does."""
     from eventlet import tpool
     tpool.QUIET = not state
+
+def hub_blocking_detection(state = False):
+    """Toggles whether Eventlet makes an effort to detect blocking
+    behavior in other code.  It does this by setting a SIGALARM with a short 
+    timeout.
+    """
+    from eventlet import hubs
+    hubs.get_hub().debug_blocking = state
+    if(not state):
+        hubs.get_hub().block_detect_post()
+    
diff --git a/eventlet/hubs/hub.py b/eventlet/hubs/hub.py
index 74efcaa..4aaf49a 100644
--- a/eventlet/hubs/hub.py
+++ b/eventlet/hubs/hub.py
@@ -2,6 +2,7 @@ import heapq
 import sys
 import traceback
 import warnings
+import signal
 
 from eventlet.support import greenlets as greenlet, clear_sys_exc_info
 from eventlet.hubs import timer
@@ -42,6 +43,11 @@ class DebugListener(FdListener):
     __str__ = __repr__
 
 
+def alarm_handler(signum, frame):
+    import inspect
+    raise RuntimeError("ALARMED at" + str(inspect.getframeinfo(frame)))
+
+
 class BaseHub(object):
     """ Base hub class for easing the implementation of subclasses that are
     specific to a particular underlying event architecture. """
@@ -62,8 +68,21 @@ class BaseHub(object):
         self.timers = []
         self.next_timers = []
         self.lclass = FdListener
-        self.debug_exceptions = True
         self.timers_canceled = 0
+        self.debug_exceptions = True
+        self.debug_blocking = False
+
+    def block_detect_pre(self):
+        # shortest alarm we can possibly raise is one second
+        tmp = signal.signal(signal.SIGALRM, alarm_handler)
+        if tmp != alarm_handler:
+            self._old_signal_handler = tmp
+        signal.alarm(1)
+    def block_detect_post(self):
+        if (hasattr(self, "_old_signal_handler") and
+            self._old_signal_handler):
+            signal.signal(signal.SIGALRM, self._old_signal_handler)
+        signal.alarm(0)
 
     def add(self, evtype, fileno, cb):
         """ Signals an intent to or write a particular file descriptor.
@@ -166,7 +185,11 @@ class BaseHub(object):
             self.stopping = False
             while not self.stopping:
                 self.prepare_timers()
+                if self.debug_blocking:
+                    self.block_detect_pre()
                 self.fire_timers(self.clock())
+                if self.debug_blocking:
+                    self.block_detect_post()
                 self.prepare_timers()
                 wakeup_when = self.sleep_until()
                 if wakeup_when is None:
diff --git a/eventlet/hubs/poll.py b/eventlet/hubs/poll.py
index 890ff50..76f5747 100644
--- a/eventlet/hubs/poll.py
+++ b/eventlet/hubs/poll.py
@@ -1,12 +1,13 @@
 import sys
 import errno
+import signal
 from eventlet import patcher
 select = patcher.original('select')
 time = patcher.original('time')
 sleep = time.sleep
 
 from eventlet.support import get_errno, clear_sys_exc_info
-from eventlet.hubs.hub import BaseHub, READ, WRITE, noop
+from eventlet.hubs.hub import BaseHub, READ, WRITE, noop, alarm_handler
 
 EXC_MASK = select.POLLERR | select.POLLHUP
 READ_MASK = select.POLLIN | select.POLLPRI
@@ -82,6 +83,11 @@ class Hub(BaseHub):
             raise
         SYSTEM_EXCEPTIONS = self.SYSTEM_EXCEPTIONS
 
+        if self.debug_blocking:
+            # shortest alarm we can possibly set is one second
+            signal.signal(signal.SIGALRM, alarm_handler)
+            signal.alarm(1)
+
         for fileno, event in presult:
             try:
                 if event & READ_MASK:
@@ -99,3 +105,7 @@ class Hub(BaseHub):
             except:
                 self.squelch_exception(fileno, sys.exc_info())
                 clear_sys_exc_info()
+        
+        if self.debug_blocking:
+            signal.alarm(0)
+
diff --git a/tests/hub_test.py b/tests/hub_test.py
index 22526f3..8eac85d 100644
--- a/tests/hub_test.py
+++ b/tests/hub_test.py
@@ -142,6 +142,17 @@ class TestHubSelection(LimitedTestCase):
             hubs._threadlocal.hub = oldhub
 
 
+class TestHubBlockingDetector(LimitedTestCase):
+    TEST_TIMEOUT = 10
+    def test_block_detect(self):
+        def look_im_blocking():
+            import time
+            time.sleep(2)
+        from eventlet import debug
+        debug.hub_blocking_detection(True)
+        gt = eventlet.spawn(look_im_blocking)
+        self.assertRaises(RuntimeError, gt.wait)
+        debug.hub_blocking_detection(False)
 
 class Foo(object):
     pass