diff --git a/gex/Client.py b/gex/Client.py
index 19b10c9..0e8eae0 100644
--- a/gex/Client.py
+++ b/gex/Client.py
@@ -1,12 +1,12 @@
 import serial
 import gex
-from gex import TinyFrame, PayloadParser, TF, PayloadBuilder
+from gex import TinyFrame, PayloadParser, TF, PayloadBuilder, TF_Msg
 
 
 class Client:
     """ GEX client """
 
-    def __init__(self, port='/dev/ttyACM0', timeout=0.3):
+    def __init__(self, port:str='/dev/ttyACM0', timeout:float=0.3):
         """ Set up the client. timeout - timeout for waiting for a response. """
         self.port = port
         self.serial = serial.Serial(port=port, timeout=timeout)
@@ -17,8 +17,31 @@ class Client:
         resp = self.query_raw(type=gex.MSG_PING)
         print("GEX connected, version string: %s" % resp.data.decode('utf-8'))
 
+        # lambda
+        def unit_repot_lst(tf :TinyFrame, msg :TF_Msg):
+            self.handle_unit_report(msg)
+            return TF.STAY
+
+        self.tf.add_type_listener(gex.MSG_UNIT_REPORT, unit_repot_lst)
+
+        self.unit_lu = {}
+        self.report_handlers = {}
+
         self.load_units()
 
+    def handle_unit_report(self, msg:TF_Msg):
+        pp = PayloadParser(msg.data)
+        callsign = pp.u8()
+        event = pp.u8()
+        payload = pp.tail()
+
+        if callsign in self.report_handlers:
+            self.report_handlers[callsign](event, payload)
+
+    def bind_report_listener(self, callsign:int, listener):
+        """ Assign a report listener function to a callsign """
+        self.report_handlers[callsign] = listener
+
     def load_units(self):
         """ Load a list of unit names and callsigns for look-up """
         resp = self.query_raw(type=gex.MSG_LIST_UNITS)
@@ -38,7 +61,7 @@ class Client:
                 'type': type,
             }
 
-    def ini_read(self):
+    def ini_read(self) -> str:
         """ Read the settings INI file """
         buffer = self.bulk_read(cs=None, cmd=gex.MSG_INI_READ)
         return buffer.decode('utf-8')
@@ -54,7 +77,7 @@ class Client:
         """ Persist INI settings to Flash """
         self.send_raw(type=gex.MSG_PERSIST_SETTINGS)
 
-    def get_callsign(self, name, type = None):
+    def get_callsign(self, name:str, type:str = None) -> int:
         """ Find unit by name and type """
         u = self.unit_lu[name]
 
@@ -67,9 +90,8 @@ class Client:
     def _write(self, data):
         """ Write bytes to the serial port """
         self.serial.write(data)
-        pass
 
-    def poll(self, attempts=10):
+    def poll(self, attempts:int=10):
         """ Read messages sent by GEX """
         first = True
         while attempts > 0:
@@ -95,7 +117,7 @@ class Client:
             else:
                 self.tf.accept(rv)
 
-    def send(self, cs, cmd, id=None, pld=None, listener=None):
+    def send(self, cmd:int, cs:int=None, id:int=None, pld=None, listener=None):
         """ Send a command to a unit. If cs is None, cmd is used as message type """
         if cs is None:
             return self.tf.query(type=cmd, id=id, pld=pld, listener=listener)
@@ -107,7 +129,7 @@ class Client:
         buf.extend(pld)
         self.tf.query(type=gex.MSG_UNIT_REQUEST, id=id, pld=buf, listener=listener)
 
-    def query(self, cs, cmd, id=None, pld=None):
+    def query(self, cmd:int, cs:int=None, id:int=None, pld=None) -> TF_Msg:
         """ Query a unit. If cs is None, cmd is used as message type """
 
         self._theframe = None
@@ -116,7 +138,8 @@ class Client:
             self._theframe = frame
             return TF.CLOSE
 
-        self.send(cs, cmd, id=id, pld=pld, listener=lst)
+        self.send(cs=cs, cmd=cmd, id=id, pld=pld, listener=lst)
+        # Wait for the response (hope no unrelated frame comes in instead)
         self.poll()
 
         if self._theframe is None:
@@ -127,15 +150,15 @@ class Client:
 
         return self._theframe
 
-    def query_raw(self, type, id=None, pld=None):
+    def query_raw(self, type:int, id:int=None, pld=None) -> TF_Msg:
         """ Query GEX, without addressing a unit """
         return self.query(cs=None, cmd=type, id=id, pld=pld)
 
-    def send_raw(self, type, id=None, pld=None):
+    def send_raw(self, type:int, id=None, pld=None):
         """ Send to GEX, without addressing a unit """
         return self.send(cs=None, cmd=type, id=id, pld=pld)
 
-    def bulk_read(self, cs, cmd, id=None, pld=None, chunk=1024):
+    def bulk_read(self, cmd:int, cs:int=None, id=None, pld=None, chunk=1024) -> bytearray:
         """ Perform a bulk read. If cs is None, cmd is used as message type """
 
         offer = self.query(cs=cs, cmd=cmd, id=id, pld=pld)
@@ -167,7 +190,7 @@ class Client:
 
         return buffer
 
-    def bulk_write(self, cs, cmd, bulk, id=None, pld=None):
+    def bulk_write(self, cmd:int, bulk, cs:int=None, id:int=None, pld=None):
         """
         Perform a bulk write. If cs is None, cmd is used as message type.
         bulk is the data to write.
diff --git a/gex/PayloadBuilder.py b/gex/PayloadBuilder.py
index c05cdb3..361ae26 100644
--- a/gex/PayloadBuilder.py
+++ b/gex/PayloadBuilder.py
@@ -5,53 +5,53 @@ class PayloadBuilder:
     Utility for building binary payloads
     """
 
-    def __init__(self, endian='little'):
+    def __init__(self, endian:str='little'):
         self.buf = bytearray()
         self.endian = endian
 
-    def close(self):
+    def close(self) -> bytearray:
         """ Get the byte buffer """
         return self.buf
 
-    def u8(self, num):
+    def u8(self, num:int):
         """ Add a uint8_t """
         self.buf.extend(num.to_bytes(length=1, byteorder=self.endian, signed=False))
 
-    def u16(self, num):
+    def u16(self, num:int):
         """ Add a uint16_t """
         self.buf.extend(num.to_bytes(length=2, byteorder=self.endian, signed=False))
 
-    def u32(self, num):
+    def u32(self, num:int):
         """ Add a uint32_t """
         self.buf.extend(num.to_bytes(length=4, byteorder=self.endian, signed=False))
 
-    def i8(self, num):
+    def i8(self, num:int):
         """ Add a int8_t """
         self.buf.extend(num.to_bytes(length=1, byteorder=self.endian, signed=True))
 
-    def i16(self, num):
+    def i16(self, num:int):
         """ Add a int16_t """
         self.buf.extend(num.to_bytes(length=2, byteorder=self.endian, signed=True))
 
-    def i32(self, num):
+    def i32(self, num:int):
         """ Add a int32_t """
         self.buf.extend(num.to_bytes(length=4, byteorder=self.endian, signed=True))
 
-    def float(self, num):
+    def float(self, num:float):
         """ Add a float (4 bytes) """
         fmt = '<f' if self.endian == 'little' else '>f'
         self.buf.extend(struct.pack(fmt, num))
 
-    def double(self, num):
+    def double(self, num:float):
         """ Add a double (8 bytes) """
         fmt = '<d' if self.endian == 'little' else '>d'
         self.buf.extend(struct.pack(fmt, num))
 
-    def bool(self, num):
+    def bool(self, num:bool):
         """ Add a bool (0 or 1) """
         self.buf.append(1 if num != False else 0)
 
-    def str(self, string):
+    def str(self, string:str):
         """ Add a 0-terminated string """
         self.buf.extend(string.encode('utf-8'))
         self.buf.append(0)
diff --git a/gex/PayloadParser.py b/gex/PayloadParser.py
index 04cd15c..951de2d 100644
--- a/gex/PayloadParser.py
+++ b/gex/PayloadParser.py
@@ -5,13 +5,13 @@ class PayloadParser:
     Utility for parsing a binary payload
     """
 
-    def __init__(self, buf, endian='little'):
+    def __init__(self, buf, endian:str='little'):
         """ buf - buffer to parse (bytearray or binary string) """
         self.buf = buf
         self.ptr = 0
         self.endian = endian
 
-    def _slice(self, n):
+    def _slice(self, n:int) -> bytearray:
         """ Extract a slice and advance the read pointer for the next slice """
         if self.ptr + n > len(self.buf):
             raise Exception("Out of bounds")
@@ -24,57 +24,57 @@ class PayloadParser:
         """ Reset the slice pointer to the beginning """
         self.ptr = 0
 
-    def tail(self):
+    def tail(self) -> bytearray:
         """ Get all remaining bytes """
         return self._slice(len(self.buf) - self.ptr)
 
-    def u8(self):
+    def u8(self) -> int:
         """ Read a uint8_t """
         slice = self._slice(1)
         return int.from_bytes(slice, byteorder=self.endian, signed=False)
 
-    def u16(self):
+    def u16(self) -> int:
         """ Read a uint16_t """
         slice = self._slice(2)
         return int.from_bytes(slice, byteorder=self.endian, signed=False)
 
-    def u32(self):
+    def u32(self) -> int:
         """ Read a uint32_t """
         slice = self._slice(4)
         return int.from_bytes(slice, byteorder=self.endian, signed=False)
 
-    def i8(self):
+    def i8(self) -> int:
         """ Read a int8_t """
         slice = self._slice(1)
         return int.from_bytes(slice, byteorder=self.endian, signed=True)
 
-    def i16(self):
+    def i16(self) -> int:
         """ Read a int16_t """
         slice = self._slice(2)
         return int.from_bytes(slice, byteorder=self.endian, signed=True)
 
-    def i32(self):
+    def i32(self) -> int:
         """ Read a int32_t """
         slice = self._slice(4)
         return int.from_bytes(slice, byteorder=self.endian, signed=True)
 
-    def float(self):
+    def float(self) -> float:
         """ Read a float (4 bytes) """
         slice = self._slice(4)
         fmt = '<f' if self.endian == 'little' else '>f'
         return struct.unpack(fmt, slice)[0]
 
-    def double(self):
+    def double(self) -> float:
         """ Read a double (8 bytes) """
         slice = self._slice(8)
         fmt = '<d' if self.endian == 'little' else '>d'
         return struct.unpack(fmt, slice)[0]
 
-    def bool(self):
+    def bool(self) -> bool:
         """ Read a bool (1 byte, True if != 0) """
         return 0 != self._slice(1)[0]
 
-    def str(self):
+    def str(self) -> str:
         """ Read a zero-terminated string """
         p = self.ptr
         while p < len(self.buf) and self.buf[p] != 0:
@@ -84,6 +84,6 @@ class PayloadParser:
         self.ptr += 1
         return bs.decode('utf-8')
 
-    def blob(self, length):
+    def blob(self, length) -> bytearray:
         """ Read a blob of given length """
         return self._slice(length)
diff --git a/gex/TinyFrame.py b/gex/TinyFrame.py
index 04403ec..df045c6 100644
--- a/gex/TinyFrame.py
+++ b/gex/TinyFrame.py
@@ -1,5 +1,5 @@
 class TinyFrame:
-    def __init__(self, peer=1):
+    def __init__(self, peer:int=1):
         self.write = None # the writer function should be attached here
 
         self.id_listeners = {}
@@ -64,7 +64,7 @@ class TinyFrame:
         else:
             raise Exception("Bad cksum type!")
 
-    def _cksum(self, buffer):
+    def _cksum(self, buffer) -> int:
         if self.CKSUM_TYPE == 'none' or self.CKSUM_TYPE is None:
             return 0
 
@@ -85,7 +85,7 @@ class TinyFrame:
         else:
             raise Exception("Bad cksum type!")
 
-    def _gen_frame_id(self):
+    def _gen_frame_id(self) -> int:
         """
         Get a new frame ID
         """
@@ -101,15 +101,15 @@ class TinyFrame:
 
         return frame_id
 
-    def _pack(self, num, bytes):
+    def _pack(self, num:int, bytes:int) -> bytes:
         """ Pack a number for a TF field """
         return num.to_bytes(bytes, byteorder='big', signed=False)
 
-    def _unpack(self, buf):
+    def _unpack(self, buf) -> int:
         """ Unpack a number from a TF field """
         return int.from_bytes(buf, byteorder='big', signed=False)
 
-    def query(self, type, listener, pld=None, id=None):
+    def query(self, type:int, listener, pld=None, id:int=None):
         """ Send a query """
         (id, buf) = self._compose(type=type, pld=pld, id=id)
 
@@ -118,11 +118,11 @@ class TinyFrame:
 
         self.write(buf)
 
-    def send(self, type, pld=None, id=None):
+    def send(self, type:int, pld=None, id:int=None):
         """ Like query, but with no listener """
         self.query(type=type, pld=pld, id=id, listener=None)
 
-    def _compose(self, type, pld=None, id=None):
+    def _compose(self, type:int, pld=None, id:int=None) -> tuple:
         """
         Compose a frame.
 
@@ -161,7 +161,7 @@ class TinyFrame:
         for b in bytes:
             self.accept_byte(b)
 
-    def accept_byte(self, b):
+    def accept_byte(self, b:int):
         # TODO this seems ripe for rewrite to avoid repetitive code
 
         if self._CKSUM_BYTES is None:
@@ -304,9 +304,9 @@ class TinyFrame:
             if rv == TF.CLOSE:
                 self.fallback_listener = None
 
-    def add_id_listener(self, id, lst, lifetime=None):
+    def add_id_listener(self, id:int, lst, lifetime:float=None):
         """
-        Add a ID listener that expires in "lifetime" ticks
+        Add a ID listener that expires in "lifetime" seconds
 
         listener function takes two arguments:
         tinyframe instance and a msg object
@@ -317,7 +317,7 @@ class TinyFrame:
             'age': 0,
         }
 
-    def add_type_listener(self, type, lst):
+    def add_type_listener(self, type:int, lst):
         """
         Add a type listener
 
diff --git a/gex/Unit.py b/gex/Unit.py
index 5208254..8b1379b 100644
--- a/gex/Unit.py
+++ b/gex/Unit.py
@@ -1,31 +1,32 @@
-from gex import Client
+from gex import Client, TF_Msg
+
 
 class Unit:
-    def __init__(self, client :Client, name :str):
+    def __init__(self, client:Client, name:str):
         self.client = client
         self.unit_name = name
         self.unit_type = self._type()
         self.callsign = client.get_callsign(name, self.unit_type)
 
-    def _type(self):
+    def _type(self) -> str:
         raise NotImplementedError("Missing _type() in Unit class \"%s\"" % self.__class__.__name__)
 
-    def send(self, cmd, pld=None, id=None):
+    def send(self, cmd:int, pld=None, id:int=None):
         """ Send a command to the unit """
         self.client.send(cs=self.callsign, cmd=cmd, pld=pld, id=id)
 
-    def query(self, cmd, pld=None, id=None):
+    def query(self, cmd:int, pld=None, id:int=None) -> TF_Msg:
         """ Query the unit. Returns TF_Msg """
-        self.client.query(cs=self.callsign, cmd=cmd, pld=pld, id=None)
+        return self.client.query(cs=self.callsign, cmd=cmd, pld=pld, id=None)
 
-    def bulk_read(self, cmd, id=None, pld=None, chunk=1024):
+    def bulk_read(self, cmd:int, pld=None, id:int=None, chunk:int=1024) -> bytearray:
         """
         Perform a bulk read.
         cmd, id and pld are used to initiate the read.
         """
-        self.client.bulk_read(cs=self.callsign, cmd=cmd, id=id, pld=pld, chunk=chunk)
+        return self.client.bulk_read(cs=self.callsign, cmd=cmd, id=id, pld=pld, chunk=chunk)
 
-    def bulk_write(self, cmd, bulk, id=None, pld=None):
+    def bulk_write(self, cmd:int, bulk, id:int=None, pld=None):
         """
         Perform a bulk write.
         cmd, id and pld are used to initiate the read.
diff --git a/main.py b/main.py
index da235c4..319e67a 100644
--- a/main.py
+++ b/main.py
@@ -9,10 +9,10 @@ if False:
     client.ini_write(s)
 
 if False:
-    buf = client.bulk_read(None, gex.MSG_INI_READ)
+    buf = client.bulk_read(gex.MSG_INI_READ)
     print(buf.decode('utf-8'))
 
-    client.bulk_write(None, gex.MSG_INI_WRITE, buf)
+    client.bulk_write(gex.MSG_INI_WRITE, buf)
 
 if True:
     led = gex.Pin(client, 'LED')