ADT's offline article gives the same pattern for each sensor: the sensor is not connected to the Base. Make sure your Base is in a central location and remove anything on or near it that could disrupt the signal; check the ADT+ app to see whether the sensor shows a strong connection; with the system disarmed and in Test Mode, remove and reinsert the battery and look for the sensor's LED;
The checks in more detail
if there is no LED, fit a new battery of the right type, a CR2 for the Door/Window Sensor, a CR123A for the Motion Sensor, three CR123A for a Smoke and CO Detector, two for a Heat Detector and so on; and if it still fails, remove the sensor and add it back in the app. ADT's low battery article lists each device's battery and says that if a low battery message does not clear after 24 hours from a replacement, you should delete and re-add the sensor.
It also notes a motion sensor may only need cleaning: residue from the battery tab can reduce contact, so open the sensor, remove the battery and clean the positive side and the contact with an alcohol swab. Sensors use ADT's own radio link, not wifi. Contact ADT chat if the sensor still will not connect. Write which sensors dropped and when, since a pattern by room often shows a metal cabinet or appliance in the way. A sensor that drops only when a large appliance runs may be near interference, so move it a hand's width.
Contact ADT chat with the sensor model and battery type ready. ADT's own article puts the Base position first in every sensor entry, so before touching a sensor, check whether anything has been stacked on or near the Base recently. If the sensor reports offline only after a storm or power cut, wait a few minutes for the Base to finish reconnecting before you remove anything, since a premature removal makes a short outage into a long job.
Differential
Likely causes of “ADT sensors and detectors is offline or unavailable”, and how to tell them apart
- 1
A weak battery
What separates it The sensor shows as offline in the app because its battery is weak and it can no longer report
How to confirm Replace the battery with the type ADT lists for that sensor and check that it reconnects
- 2
A Base too far away
What separates it The connection to the Base is weak because the sensor is a long way from the Base or behind thick walls
How to confirm Move the Base or the sensor closer together and check the signal strength in the app
- 3
Objects on the Base
What separates it The signal is blocked because objects are stacked on or right beside the Base, weakening its radio link
How to confirm Clear the Base so nothing sits on or against it, then see whether the sensor comes back online
- 4
A dirty battery contact
What separates it A low battery message stays on even after a battery change because the battery contact is dirty
How to confirm Clean the battery contacts gently with an alcohol swab, let them dry, then refit the battery
- 5
A stuck sensor
What separates it The sensor will not reconnect at all after a battery change or a move and stays offline
How to confirm Remove the sensor from the app and add it again as a new device beside the Base
Before you touch a setting
Record this first — changing settings destroys the evidence
- Which sensor is offline and what type of battery it uses
- The signal strength shown for the sensor in the app
- Where the Base is placed and what is near it
- What the sensor's LED does when you press or trigger it
Try in this order
0 of 7 completedDisarm and enter Test Mode
ReversibleDisarm the system and put it into Test Mode before troubleshooting, so that nothing you do sets off a real alarm.
Check the Base position
ReversibleCheck the Base position, which should be central and clear of clutter, because the sensor's radio link ends at the Base.
Check the signal in the app
ReversibleCheck the signal in the app for the sensor, where a strong connection means the radio link is healthy and the fault lies elsewhere.
Reseat or replace the battery
ReversibleReseat or replace the battery with the right type, making sure it sits the right way round and makes firm contact.
Clean contacts
ReversibleClean the battery contacts with an alcohol swab and let them dry, since dirt on the contacts can cause a low battery message that never clears.
Remove and re-add
ReversibleRemove the sensor and add it again in the app, pairing it beside the Base, if it still will not reconnect.
Contact ADT
ReversibleContact ADT if it stays offline after these steps, and tell them the sensor type, its battery and how far it is from the Base.
Model-specific
What is true of this model and not of its siblings
- Motion sensor
- Uses one CR123A battery.
- Door and window sensor
- Uses one CR2 battery.
- Other models this page answers
- These steps also fit models Carbon Monoxide Detector, Indoor Siren, Live Light, Smoke and Carbon Monoxide Detector, Smoke Detector.
Stop boundary
When this stops being a self-service repair
- !If it stays offline after a new battery and re-add, contact ADT through chat
- !If several sensors drop offline together, check the Base rather than the individual sensors
- !If a battery message persists 24 hours after change, re-add the sensor
Evidence ledger
Sources behind this answer
Offline meaning and fixes per device.
Battery types and lives.
Motion sensor setup and use.
Removing and adding devices.
The company and its products.
Exact questions
Common questions
What does offline mean for a sensor?+
Offline for a sensor means it is not connected to the Base, so the Base cannot see its status and no alarm from that sensor will be reported.
What should the system be in?+
The system should be disarmed and in Test Mode while you troubleshoot, so that triggering a sensor does not start a real alarm.
What if there is no LED?+
If the sensor's LED does not light at all, fit a new battery, because a dead or missing battery is the commonest reason for a silent sensor.
What if a battery message does not clear?+
If a battery message does not clear after replacement, delete the sensor and add it again after 24 hours so its status resets cleanly.
Can cleaning help?+
Yes, cleaning can help, particularly for motion sensors whose lens and battery contacts collect dust and can cause faults.
Do sensors use wifi?+
No, ADT sensors do not use wifi; they talk to the Base over ADT's own radio link, and only the Base uses your home wifi.
Should the Base be central?+
Yes, the Base should be in a central place, so that the radio link reaches every sensor around the home with a strong signal.
What battery does the Door/Window Sensor use?+
The Door and Window Sensor uses one CR2 lithium battery, which is fitted behind the cover of the sensor.
What does the Water and Temperature Sensor use?+
The Water and Temperature Sensor uses one CR123A battery, the same type as the Motion Sensor.