diff --git a/timed-ble-beacon b/timed-ble-beacon
index 79d032b8..d69ed6e4 100755
--- a/timed-ble-beacon
+++ b/timed-ble-beacon
@@ -103,29 +103,31 @@ class BLEAdMsg(dbus.service.Object): # see man org.bluez.LEAdvertisement
 	m = ( lambda si='',so='',iface='org.freedesktop.DBus.Properties':
 		dbus.service.method(iface, in_signature=si, out_signature=so) )
 
-	def __init__(self, bus, mid, secret, td, n=None):
-		n, td = n or int(time.time() - 1_735_689_600), round(td / 100)
+	def __init__(self, bus, mid, secret, td, bms_a, bms_b):
+		n, td = int(time.time() - 1_735_689_600), round(td / 100)
 		msg = struct.pack('<HL', td, n)
 		mac = hmac.HMAC(secret, msg, digestmod=hl.sha256).digest()[:20]
 		ad_name = base64.urlsafe_b64encode(mac).decode()
 		ad_name = ad_name.translate(dict(zip(b'_-=', 'qQX'))) # dbus name limits
 		self.bus, self.path = bus, f'/org/bluez/example/advertisement/{ad_name}'
 		p(f'-- new BLE ad [ {self.path} ]: ( {mid:,d}, {td:,d} {n:,d} {secret} )')
-		self.data = dbus.Dictionary( # uint16 key, <=27B value
-			{mid: dbus.Array(msg + mac, signature='y')}, signature='qv' )
+		self.broadcast = dict(
+			MinInterval=dbus.UInt32(bms_a), MaxInterval=dbus.UInt32(bms_a),
+			ManufacturerData=dbus.Dictionary( # uint16 key, <=27B value
+				{mid: dbus.Array(msg + mac, signature='y')}, signature='qv' ) )
 		super().__init__(self.bus, self.path)
 
 	@m('s', 'a{sv}')
 	def GetAll(self, iface):
 		try:
 			if iface != self.iface: raise BLErrInvalidArgs
-			return dict(Type='broadcast', ManufacturerData=self.data)
+			return dict(Type='broadcast', **self.broadcast)
 		except: tb.print_exc(file=sys.stderr); sys.stderr.flush()
 	Get = m('ss', 'v')(lambda s, iface, k: s.GetAll(iface)[k])
 	Release = m(iface=iface)(lambda s: None)
 
 
-def run_ad(mid, secret, td_updates, td_total):
+def run_ad(mid, secret, td_updates, td_total, td_beacon):
 	ts_end = time.monotonic() + td_total
 	dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
 	bus = dbus.SystemBus()
@@ -147,7 +149,7 @@ def run_ad(mid, secret, td_updates, td_total):
 				except: pass
 				if close: return
 			if not (td := max(0, ts_end - time.monotonic())): return loop.quit()
-			ad = BLEAdMsg(bus, mid, secret, td)
+			ad = BLEAdMsg(bus, mid, secret, td, *td_beacon)
 			ad_mgr.RegisterAdvertisement( ad.path, {},
 				reply_handler=lambda: None, error_handler=lambda err:
 					(p_err(f'BLE ad setup/update failed - {err}' ), loop.quit()) )
@@ -155,8 +157,8 @@ def run_ad(mid, secret, td_updates, td_total):
 		except: tb.print_exc(file=sys.stderr); sys.stderr.flush(); loop.quit()
 
 	ts_start = dt.datetime.now().isoformat(sep=' ', timespec='seconds')
-	p( f'loop: Setup start=[ {ts_start} ]'
-		f' duration=[ {ts_repr(td_total)} ] update-interval=[ {ts_repr(td_updates)} ]' )
+	p( f'loop: Setup start=[ {ts_start} ] duration=[ {ts_repr(td_total)} ]'
+		f' update-interval=[ {ts_repr(td_updates)} ] beacon_ms={td_beacon}' )
 	loop = GLib.MainLoop()
 	for sig in signal.SIGTERM, signal.SIGINT:
 		GLib.unix_signal_add(GLib.PRIORITY_DEFAULT, sig, loop.quit)
@@ -200,6 +202,10 @@ def main(argv=None):
 			Interval between updating BLE broadcast data. Default: %(default)s
 			Same exact broadcast is repeated within these intervals.
 			Should be specified as a relative short time (e.g. 1m45s) or [[HH:]MM:]SS.'''))
+	parser.add_argument('-b', '--beacon-interval',
+		metavar='ms[-ms]', default='60-120', help=dd('''
+			Range for an interval between sending beacons
+				when those are active, in milliseconds. Default: %(default)s'''))
 
 	parser.add_argument('--mid', metavar='uint16', type=int, default=61_634, help=dd('''
 		Manufacturer "Company Identifier" field in 0-65535 range. Default: %(default)s
@@ -223,7 +229,11 @@ def main(argv=None):
 
 	if not opts.debug: global p; p = lambda *a,**kw: None
 	if not opts.time_span: parser.error('-t/--time-span option must be specified')
+
+	bms_a, s, bms_b = map(str.strip, opts.beacon_interval.partition('-'))
+	bms_a, bms_b = int(bms_a or bms_b), int(bms_b or bms_a)
 	run_ad( opts.mid, _read_file(opts.secret).encode(),
+		td_beacon=(bms_a, bms_b),
 		td_total=ts_parse(opts.time_span).total_seconds(),
 		td_updates=ts_parse(opts.update_interval, relative_only=True).total_seconds() )
 
diff --git a/timed-ble-beacon-mpy-led b/timed-ble-beacon-mpy-led
index 817349fa..0d02cda6 100644
--- a/timed-ble-beacon-mpy-led
+++ b/timed-ble-beacon-mpy-led
@@ -7,20 +7,21 @@ import asyncio, machine, bluetooth, time, struct, random
 class Conf:
 	verbose = False
 	ble_mid = 61_634 # uint16 manufacturer id to match in broadcasts
-	ble_secret = b'timed-beacon-test'
+	ble_secret = b'timed-beacon-test' # HMAC key
 
-	scan_duration_ms = 5_000
+	# 5s ~ 55x 30ms 30%dc listen-intervals
 	scan_interval_us = 60_000
 	scan_window_us = 30_000
 
-	# "clear" is the normal state, "beacon" is a state when those are detected
-	clear_sample_interval = 20.0
-	clear_sample_time = 4.0
-	beacon_sample_interval = 5.0 * 60 # won't get lower than this in a "beacon" state
+	# "clear" is the normal state, "beacon" is a state when valid beacons are detected
+	clear_sample_time = 4.0 # seconds to run BLE scan for, with duty cycle scan_* opts
+	clear_sample_interval = 20.0 # sleep delay between scans
 	beacon_sample_time = 3.0
+	beacon_sample_interval = 5.0 * 60 # won't get lower than this in a "beacon" state
 	beacon_repeat_grace = 6.0 * 60 # ok to repeat counter within this td
-	beacon_span_checks = 6 # do N checks within timespan sent in the beacon
+	beacon_span_checks = 6 # wakeup for N checks within timespan sent in the beacon
 
+	# led_time values are scanned with random chance, interval picked from min-max
 	_tdt = cs.namedtuple('LEDtdt', 'chance time_min time_max')
 	led_pin = 'LED'
 	led_time_on = [_tdt(1, 0.020, 1.0)]
@@ -30,16 +31,18 @@ class Conf:
 
 class BLE_MSE_Scanner:
 
-	def __init__(self, duration_ms, interval_us, window_us):
-		self.ble, self.scan_args = bluetooth.BLE(), (duration_ms, interval_us, window_us)
-		self.ble.irq(self._irq_handler)
+	def __init__(self, interval_us, window_us):
+		self.scan_td, self.scan_dc = 5_000, (interval_us, window_us)
 		self.scan, self.queue, self.check = False, list(), asyncio.ThreadSafeFlag()
+		self.ble = bluetooth.BLE()
+		self.ble.irq(self._irq_handler)
 
+	def duration(self, duration_ms):
+		self.scan_td = duration_ms; return self
 	def __enter__(self):
 		if self.scan: raise RuntimeError('Concurrent scans not allowed')
 		self.scan = True; self.queue.clear(); self.check.clear()
-		self.ble.active(True); self.ble.gap_scan(*self.scan_args)
-
+		self.ble.active(True); self.ble.gap_scan(self.scan_td, *self.scan_dc)
 	def __exit__(self, *err):
 		self.scan = False; self.check.set(); self.ble.active(False)
 
@@ -113,8 +116,7 @@ async def run_ble(conf, leds):
 			(conf.clear_sample_interval, conf.clear_sample_time) ) )))
 	beacon_grace_td = round(conf.beacon_repeat_grace * 1000)
 	p_log = conf.verbose and (lambda *a: print('[main]', *a))
-	ble_scan = BLE_MSE_Scanner(
-		conf.scan_duration_ms, conf.scan_interval_us, conf.scan_window_us )
+	ble_scan = BLE_MSE_Scanner(conf.scan_interval_us, conf.scan_window_us)
 
 	p_log and p_log('Starting main loop...')
 	counter, st = 0, st_clear; td_sleep, td_sample = timings[st]
@@ -144,7 +146,7 @@ async def run_ble(conf, leds):
 		p_log and p_log(f'Scanning for broadcasts ({td_sample:,d}ms)...')
 		beacon = False
 
-		with ble_scan: # scan until first hmac-match
+		with ble_scan.duration(td_sample): # scan until first hmac-match
 			while data := await ble_scan.get_data():
 				if len(data) != 28 or int.from_bytes(data[:2], 'little') != conf.ble_mid: continue
 				data, hmac = data[2:8], data[8:]