diff --git a/frigate/test/test_builtin.py b/frigate/test/test_builtin.py
new file mode 100644
index 0000000000..4c9db6140d
--- /dev/null
+++ b/frigate/test/test_builtin.py
@@ -0,0 +1,53 @@
+"""Tests for frigate.util.builtin helpers."""
+
+import unittest
+from unittest.mock import patch
+
+from frigate.util.builtin import EventsPerSecond
+
+
+class TestEventsPerSecond(unittest.TestCase):
+    def test_eps_is_zero_before_any_events(self) -> None:
+        eps = EventsPerSecond()
+        with patch("frigate.util.builtin.time.monotonic", return_value=100.0):
+            self.assertEqual(eps.eps(), 0.0)
+
+    def test_eps_counts_events_in_window(self) -> None:
+        eps = EventsPerSecond(last_n_seconds=10)
+        clock = [1000.0]
+        with patch("frigate.util.builtin.time.monotonic", side_effect=lambda: clock[0]):
+            eps.start()
+            # one event per second for five seconds
+            for _ in range(5):
+                clock[0] += 1.0
+                eps.update()
+            # five events over the five seconds since start
+            self.assertAlmostEqual(eps.eps(), 1.0)
+
+    def test_old_timestamps_expire_from_window(self) -> None:
+        eps = EventsPerSecond(last_n_seconds=10)
+        clock = [0.0]
+        with patch("frigate.util.builtin.time.monotonic", side_effect=lambda: clock[0]):
+            eps.start()
+            for _ in range(10):
+                clock[0] += 1.0
+                eps.update()
+            # jump well past the window so every timestamp ages out
+            clock[0] += 100.0
+            self.assertEqual(eps.eps(), 0.0)
+
+    def test_timestamps_are_memory_bounded(self) -> None:
+        # last_n_seconds large enough that nothing expires by time, so the
+        # maxlen cap is what bounds retention
+        eps = EventsPerSecond(max_events=5, last_n_seconds=10_000)
+        clock = [0.0]
+        with patch("frigate.util.builtin.time.monotonic", side_effect=lambda: clock[0]):
+            eps.start()
+            for _ in range(1000):
+                clock[0] += 0.001
+                eps.update()
+            self.assertLessEqual(len(eps._timestamps), 5)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/frigate/util/builtin.py b/frigate/util/builtin.py
index c1c9d9d6ea..288ecd3c7c 100644
--- a/frigate/util/builtin.py
+++ b/frigate/util/builtin.py
@@ -2,7 +2,6 @@
 
 import ast
 import copy
-import datetime
 import logging
 import math
 import multiprocessing.queues
@@ -10,7 +9,9 @@ import queue
 import re
 import shlex
 import struct
+import time
 import urllib.parse
+from collections import deque
 from collections.abc import Mapping
 from multiprocessing.managers import ValueProxy
 from pathlib import Path
@@ -32,23 +33,20 @@ class EventsPerSecond:
         self._start = None
         self._max_events = max_events
         self._last_n_seconds = last_n_seconds
-        self._timestamps = []
+        self._timestamps: deque[float] = deque(maxlen=max_events)
 
     def start(self) -> None:
-        self._start = datetime.datetime.now().timestamp()
+        self._start = time.monotonic()
 
     def update(self) -> None:
-        now = datetime.datetime.now().timestamp()
+        now = time.monotonic()
         if self._start is None:
             self._start = now
         self._timestamps.append(now)
-        # truncate the list when it goes 100 over the max_size
-        if len(self._timestamps) > self._max_events + 100:
-            self._timestamps = self._timestamps[(1 - self._max_events) :]
         self.expire_timestamps(now)
 
     def eps(self) -> float:
-        now = datetime.datetime.now().timestamp()
+        now = time.monotonic()
         if self._start is None:
             self._start = now
         # compute the (approximate) events in the last n seconds
@@ -63,7 +61,7 @@ class EventsPerSecond:
     def expire_timestamps(self, now: float) -> None:
         threshold = now - self._last_n_seconds
         while self._timestamps and self._timestamps[0] < threshold:
-            del self._timestamps[0]
+            self._timestamps.popleft()
 
 
 class InferenceSpeed: