They report an opening, which is earlier than reporting a presence
A contact sensor is two parts — a switch and a magnet — and it reports the moment a door or window starts to open, which is earlier and less ambiguous than a motion detector reporting that someone is already inside. The specification that decides whether it works on your window is the gap tolerance: how far the magnet can sit from the switch before the contact drops: 7 to 20 mm (0.28 to 0.79 in) for the sensors in this hub that publish it. Metal frames can complicate this, and some sensors state a reduced gap on steel. We compare gap tolerance, battery type and stated life, radio protocol, tamper detection and metal frame behavior.
Standalone magnetic contact · remote control · up to 8 remotes per sensor · chime or alarm
A standalone magnetic door and window alarm with a remote control, which HENDUN states can be paired with up to eight remotes per sensor, and used as a chime as well as an alarm.
Best for: A single door — a shed, a gate, an internal door — that should announce itself with no system behind it.
≈ $10
THE ONLY GAP FIGURE ON THIS SHELF: the magnet must sit no more than 0.6 in — 15.2 mm (0.60 in) — from the alarm · 90 dB standalone siren, alerts nobody remotely · 2 AAA, not included · 3.4 × 1.1 × 0.6 in · dust-proof, stated for humidity and extreme temperatures · pack count not published
The only listing on this shelf that publishes the one measurement the shelf says decides everything.
Best for: Any window whose recess you have measured — this is the only sensor here you can check against it
≈ $10
6-pack · standalone · trigger at a 2 cm (0.8 in) gap · 3 volume levels · 3 modes · adhesive mounting
A pack of six standalone door and window alarms that TECKNET states trigger when the two halves separate by more than 2 cm (0.8 in), with three volume levels and three modes, mounted with the supplied adhesive pads.
Best for: A window, a shed or a sliding door where a local noise is the whole requirement.
90 dB standalone siren · 3.54 × 1.18 × 0.79 in and about 0.08 lb, both published · 2 AAA, NOT included · a three-step install written out · five units for ten dollars · no gap figure, no battery life, no tamper detection
Five alarms for ten dollars with their dimensions and weight published — two figures the cheapest sirens here usually leave out.
Best for: Five openings on a tight budget, where the body has to be measured against a shallow frame first
≈ $10
120 dB alarm or chime, switched on the side: OFF / chime / alarm · 4 LR44 cells SUPPLIED · a battery TEST BUTTON and a low-battery LED, the only test button on this shelf · double-sided tape included · no gap figure, no battery life, no tamper detection
The only sensor here with a button that tells you the battery is still good — which on an alarm nobody checks is worth more than it sounds.
Best for: A household that wants a chime for the back door in the day and an alarm on it at night
≈ $19
125 dB, the loudest on this shelf, with 100 dB and 100 dB chime modes · a 31-second alarm that will not stop until the opening is closed · 3 LR44 cells SUPPLIED · up to 13 months of stated life · low-battery indicator · no gap figure
The loudest, the most configurable and the only one here with both supplied batteries and a stated life — three modes, 125 dB and thirty-one seconds.
Best for: A pool gate, a medicine cabinet or a front door where the volume and the mode need to differ by room
≈ $34
Six system sensors that alert a phone, not a siren on the frame · approximately 3-year battery life, the longest published here · two 3 V CR2032 cells included per sensor · REQUIRES a Ring Alarm Base Station · mobile alerts require a Ring Protect subscription · no gap figure, no protocol, no tamper detection
Six sensors that tell your phone rather than the street — on condition you already own a base station and pay a subscription.
Best for: A house that already has a Ring Alarm base station and six more openings to cover
≈ $60
FIFTEEN alarms in one box, the largest pack on this shelf — about a dollar forty each · 90 dB standalone siren, alerts nobody remotely · 2 AAA, NOT included · dust-proof · no gap figure, no dimensions, no battery life, no tamper detection
Fifteen alarms for twenty-one dollars, which is the cheapest way on this shelf to put something on every opening in a house.
Best for: A whole house, a vacation rental or a small office where every window should make a noise and nothing needs an app
≈ $21
Wi-Fi 2.4 GHz direct, no bridge · Tuya · 70 × 25 mm (2.76 × 0.98 in) and 11 × 44 mm (0.43 × 1.73 in) · 2 × AAA · adhesive
A Wi-Fi door sensor that connects straight to the router with no bridge or hub, on the Tuya platform. Sone publishes both module sizes and states adhesive mounting on two AAA cells.
Best for: One or two doors, in a house with no hub and no intention of getting one.
Zigbee · tamper alarm · local scenes without cloud · requires a Zigbee hub
A Zigbee door and window sensor with a tamper alarm, which SONOFF states can run local scenes between Zigbee devices without the internet — provided a compatible hub is present.
Best for: A Zigbee household — Home Assistant, SmartThings or SONOFF's own hub — wanting cheap, reliable contacts.
NO BASE STATION REQUIRED — connects over Amazon Sidewalk, the only named network on this shelf · six sensors · 24/7 professional monitoring on a subscription · no battery type, no battery life, no gap figure, no tamper detection
The only sensor on this shelf that needs no hub at all — and the only one that names the network it talks to.
Best for: A house with no alarm system that wants phone alerts on six openings and nothing else to buy
≈ $80
For Smartvest Pro · wireless opening detector · triggers configured scenarios · doors and windows
The opening detector for ABUS's Smartvest Pro alarm. It reports unauthorized opening of doors, windows and patio doors, and triggers whatever scenarios have been configured on the panel.
Best for: An ABUS Smartvest Pro system being extended door by door.
One sensor per accessible opening is the principle of the device. The TECKNET pack puts six alarms in one box; the SONOFF also needs a Zigbee hub. In exchange, the TECKNET only sounds on the spot and sends nothing to your phone.
A sensor that needs less than five millimeters of gap triggers on its own on a window that moves in the wind. The stated maximum gap decides the number of false alarms a month.
Changing eight cells a year across eight openings turns monitoring into a chore and ends in silent sensors. The stated battery life decides the real reliability of a whole system.
No: it detects the two parts moving apart, so an opening. A pane broken without opening the window does not trigger it.
A maximum dimension is stated and has to be respected. Beyond it, the sensor reports a permanent opening.
Metal disturbs some magnetic sensors. Spacers or suitable models exist.
Yes: every unequipped opening is an unwatched way in. That is the very principle of the device.
Often several years. The low-battery warning is what prevents a sensor silently out of service.
On a clean, degreased surface, generally well. Temperature variations and damp lift it in the long run.
That is precisely its point: protecting the openings while you are inside, which a volume detector does not allow.
The adhesive holds on a clean, degreased profile, but aluminum can disturb the radio range if the transmitter is recessed. Surface mounting, a few centimeters away from the metal, usually solves it.
The sensor detects opening, never breaking: a pane broken without opening the window does not trigger it. Respect the gap dimension, degrease before sticking — and the low-battery warning is what prevents a sensor silent for months.
A characteristic has to come from four devices in five to hold a column. Below that, we would be lining up empty cells.
| Model | Price | Mounting | Type |
|---|---|---|---|
| KOLODOGO Door and window alarm, 5-pack, 90 dB, 3.54 × 1.18 × 0.79 in | $10 | A three-step install written out: insert two AAA cells, peel and stick, turn on the switch — stated, with no tools needed | A standalone alarm: the magnetic sensor triggers a 90 dB siren in the unit itself, and nothing is reported remotely. No app, no radio, no base station — Wireless in the title means no cable to run |
| PLOJOP Door and window alarm, 90 dB, 3.4 × 1.1 × 0.6 in | $10 | Peel-and-stick double-sided tape, with an on/off switch pressed before the cells go in — stated. No screw option | A standalone alarm, not a system sensor: the two parts separate, the unit screams at 90 dB where it is fitted, and nothing is reported anywhere else. The word Wireless in the title means no cable to run, not a radio link |
| HENDUN SZSF03R | $10 | — | Standalone magnetic contact alarm |
| Philips LRM3320W/27 window and door alarm, 4-pack, 120 dB with chime mode | $19 | Double-sided tape included, stated as completely wire and hassle-free, with everything needed in the box | A standalone alarm with a magnetic sensor: it sounds where it is fitted and reports nothing remotely. No app, no radio, no base station |
| WimuPath Door and window alarm, 15-pack, 90 dB | $21 | Adhesive, with an on/off switch pressed before the cells go in, then the double-sided tape peeled and the unit stuck to the frame — stated | A standalone alarm: the magnetic switch detects the opening, the unit sounds at 90 dB where it is stuck, and nothing is reported anywhere else. No app, no radio, no base station |
| SanJie YYDOA01 door and window alarm sensors, 5-pack, 125 dB with volume control | $34 | 3M double-sided tape on the back, with the switch set after sticking. SanJie recommends installing indoors — the only placement advice on this shelf | A standalone alarm: the magnet separates, the unit sounds where it is fitted, and nothing is reported remotely. No app, no radio, no base station |
| Ring Alarm Contact Sensor 6-pack, 2nd generation | $60 | Mounts to door and window frames with no tools required, stated. The second generation is stated to be smaller than the first, which Ring says enables more placement options | A system contact sensor, not a standalone alarm. It makes no noise of its own: the opening is reported to the base station, which sounds the siren and raises the alert. At least five of the twelve sensors on this shelf are the opposite — a screamer on the frame reporting to nobody |
| Ring Window and Door Sensor (newest model), 6-pack, no base station | $80 | Mounts in minutes with no tools and no wiring, stated | A system sensor that reports to an app rather than sounding where it is fitted. No local siren |
| ABUS FUMK45000 | — | — | Wireless opening detector |
| SONOFF SNZB-04P | — | Two 3M adhesive pads supplied | — |
| Sone Smart One SB589 | — | Double-sided adhesive | — |
| TECKNET TK-WA801 | — | Adhesive pads supplied | Standalone door and window alarms, pack of 6 |
$10 – $10
2 models
KOLODOGO Door and window alarm, 5-pack, 90 dB, 3.54 × 1.18 × 0.79 in, PLOJOP Door and window alarm, 90 dB, 3.4 × 1.1 × 0.6 in
$10 – $19
2 models
HENDUN SZSF03R, Philips LRM3320W/27 window and door alarm, 4-pack, 120 dB with chime mode
Specifications: manufacturer sheets for home security products and the matching Amazon product pages. Prices and availability: Keepa. Every figure in this table names its source.
Most recent revision in this category: October 8, 2026.
Prices quoted in these summaries are dated readings. The live price is shown next to each product.
