Contact status
Shows whether the monitored door, window or other contact is currently open or closed.
Getting started
Complete the initial setup before fixing Sentra permanently in position.
Insert the batteries
Insert three AAA batteries, observing the polarity markings inside the battery compartment.
Switch Sentra on
Move the power switch to the ON position.
Keep the magnet away during setup
Keep the supplied magnet away from the marked side of Sentra so the contact remains open and the device stays awake while you configure it.
Connect Sentra to Wi-Fi
Follow the Wi-Fi instructions below, then test the alarm and phone notification before mounting the device.
Physical installation
Sentra and its magnet must move apart when the monitored contact is opened.
Choose the position
Place Sentra on the fixed or moving surface and position the magnet beside the edge marked with the magnet symbol.
Check the alignment
With the contact closed, place the magnet as close as possible to Sentra without allowing the two parts to touch.
Attach the cradle
Clean and dry the mounting surface. Remove the backing from the adhesive pad and press the cradle firmly into position.
Fit Sentra
Slide Sentra into the cradle and secure the magnet in its chosen position. Open and close the contact to confirm that the status changes correctly.
Do not install Sentra where it will be exposed to water, condensation,
extreme heat or direct outdoor weather unless your model is specifically rated for that location.
Connecting to Wi-Fi
When no Wi-Fi details are stored, Sentra creates its own temporary setup network.
Open your phone's Wi-Fi settings
Connect to the Wi-Fi network created by Sentra. The network name may appear as Sentra Setup.
Open the setup page
The page may open automatically. Otherwise, open a browser and visit
http://sentrab.local. If that does not work, use
http://192.168.4.1.
Select your home network
Scan for nearby Wi-Fi networks, select your home network and enter its password carefully.
Save and reconnect
Save the settings. Sentra will restart and connect to your home Wi-Fi. Reconnect your phone to its usual Wi-Fi network afterwards.
Sentra uses 2.4 GHz Wi-Fi. Some routers combine 2.4 GHz and 5 GHz under
one network name; this normally works without any changes.
Using notifications
Sentra uses the free ntfy service to send alerts directly to your phone. No Home Assistant installation or paid subscription is required.
Install ntfy
Install the ntfy app from the Apple App Store or Google Play Store.
Add your Sentra topic
Open ntfy, add a new subscription and enter the unique topic supplied with your Sentra device.
Allow notifications
Allow notification permissions when requested by your phone.
Send a test
Open Sentra's built-in web interface and press the notification test button. Confirm that the test alert reaches your phone.
Treat your ntfy topic name as private. Anyone who knows the exact topic
may be able to subscribe to messages sent to it.
Sentra web interface
Open the monitored contact to wake Sentra, then visit
http://sentrab.local from a device connected to the same Wi-Fi network.
Battery level
Displays the estimated remaining battery level. Replace all three batteries when the level becomes low.
Wi-Fi status
Shows whether Sentra is connected, together with available network and signal information.
Notification test
Sends an immediate test message to confirm that ntfy is configured and working.
Alarm delay
Sets how long the contact may remain open before the buzzer and notification are triggered.
Reminder interval
Sets how often Sentra repeats its alert while the monitored contact remains open.
Wi-Fi configuration
Allows compatible firmware versions to scan for and connect to a different Wi-Fi network.
Restart and firmware details
Depending on the installed firmware, the page may also show the firmware version or provide a restart control.
Normal operation
Once setup is complete, Sentra operates automatically.
The contact opens
Sentra wakes and starts the configured alarm timer.
The delay expires
If the contact is still open, Sentra sounds its buzzer and sends an ntfy notification.
Reminders continue
Further alerts are sent at the configured interval until the contact is closed.
The contact closes
Sentra waits briefly, then returns to its low-power sleep mode to conserve the batteries.
Battery replacement
Sentra is powered by three AAA batteries.
Switch Sentra off
Move the power switch to OFF before opening the battery compartment.
Replace all three batteries
Remove the old batteries and install three new batteries of the same type and brand.
Check the polarity
Match the positive and negative ends to the markings inside the compartment.
Switch Sentra on
Confirm that Sentra reconnects and that its contact status is shown correctly.
Do not mix old and new batteries or different battery types. Remove the
batteries if Sentra will be stored unused for a long period.
Troubleshooting
I cannot see the Sentra setup Wi-Fi network
Confirm that Sentra is switched on and that the magnet is away from the marked side. If Wi-Fi credentials are already stored, Sentra may be trying to connect to that network rather than opening setup mode.
The setup page does not open automatically
While connected to the Sentra setup network, open
http://192.168.4.1 manually in your browser.
sentrab.local does not open
Make sure your phone is connected to the same home Wi-Fi network as Sentra and that the monitored contact is open so Sentra is awake. Some networks do not support local names reliably.
Sentra will not connect to my Wi-Fi
Check the Wi-Fi password and confirm that 2.4 GHz Wi-Fi is enabled. Move Sentra closer to the router during setup.
I do not receive phone notifications
Confirm that the ntfy topic matches the one supplied with your device, notification permission is enabled, and your phone has an internet connection. Then use the test notification button.
The contact status is incorrect
Move the magnet closer to the side marked with the magnet symbol. Check that the magnet lines up with Sentra when the monitored contact is closed.
The batteries are running down quickly
Weak or unavailable Wi-Fi can keep the device awake for longer. Check the signal strength, magnet alignment and that the contact is normally closed when not in use.
Frequently asked questions
Does Sentra require Home Assistant?
No. Sentra connects directly to Wi-Fi and uses ntfy for phone notifications.
Is a subscription required?
No paid Sentra subscription is required.
What can Sentra monitor?
Sentra can monitor doors, windows, gates, cupboards, cabinets, fridges, freezers and many other access points.
Will the buzzer work without internet access?
Yes. The local buzzer can still operate, but phone notifications require internet access.
Can several phones receive alerts?
Yes. Install ntfy on each phone and subscribe each device to the same Sentra topic.
Is Sentra suitable for outdoor use?
The standard Sentra enclosure is intended for indoor use unless your specific model is marked otherwise.