They report an opening, which is earlier than reporting a presence · review
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.
The conclusion A noise on one door, for very little. Test the gap before sticking it down.
The simplest device in this hub: a magnet, a switch, a battery and a siren.
One door. A shed, a gate, an internal door to a room that should stay shut. It makes a noise when the magnet leaves the switch, and nothing else happens.
That is enough when somebody is nearby, and it is nothing at all when the building is empty. Standalone contacts do not add up to a system, however many you buy — a system needs a hub that knows which sensor fired and can tell you about it.
Unusual and useful on a shared entrance: everyone who needs to open the gate gets a fob, and nobody needs to be added to an app. It is the same problem a combination lock solves, and the same caution applies — eight remotes is eight things that can be lost, and there is no way to revoke one.
Gap tolerance. Every contact sensor holds its switch closed with a magnet, and how far apart the two halves can sit before it opens — usually 10 to 25 mm (0.39 to 0.98 in) — decides whether it works on your door. It is not stated here.
Test it in position, holding both halves in place, before peeling the adhesive. A vinyl window that closes onto a deep recess defeats sensors rated for a small gap, and it fails on a windy night rather than on the day you fit it.
A gate, a shed, or one door in a house.
On sale at $10 on the American Amazon store at the time of checking.
Prices and availability are what Keepa reported on the date this page was updated; both move.
Prices quoted in this text were read on September 2, 2026. The live price is at the top of the page.
| Type | Standalone magnetic contact alarm |
|---|---|
| Control | Remote control; up to 8 remotes per sensor |
| Modes | Alarm, chime or doorbell |
| Applications | Doors, gates, windows, pool gates, per HENDUN |
| Alarm | 105 dB, fixed volume, low-battery indicator, stated by HENDUN |
| Amazon reference | B07J449TKB |
| EAN | 0664248681751 |
For a gate used by a family or a small business, where everybody needs to be able to disarm it. It is the same problem a combination padlock solves, applied to an alarm — and it is genuinely useful on a shared entrance.
On one specific door, yes. A shed, a gate, an internal door to a room that should stay shut. It makes a noise where it is, which is enough when somebody is nearby and nothing at all when they are not.
Not published. Contact sensors work by holding a switch closed with a magnet, and the gap they tolerate — usually somewhere between 10 and 25 mm (0.98 in) — decides whether they suit your door. Test it in place before committing the adhesive.
6.9/ 10
A noise on one door, for very little. Test the gap before sticking it down.
Between security devices of the same category and nearby price. Shown: what they all state. A half-filled column says nothing.
| Model | Price | Type |
|---|---|---|
| HENDUN SZSF03R | $10 | Standalone magnetic contact alarm |
| KOLODOGO Door and window alarm, 5-pack, 90 dB, 3.54 × 1.18 × 0.79 in | $10 | 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 | 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 |
| Philips LRM3320W/27 window and door alarm, 4-pack, 120 dB with chime mode | $19 | A standalone alarm with a magnetic sensor: it sounds where it is fitted and reports nothing remotely. No app, no radio, no base station |
A reference exists on these Amazon stores: France, Germany, Spain, United Kingdom, United States. Listed is not the same as in stock — availability changes daily.
Details checked on September 2, 2026.
A single door — a shed, a gate, an internal door — that should announce itself with no system behind it.
Amazon reports what buyers took in the month before this page was last checked: at least 100.
The figure is a floor, rounded by Amazon, and read through Keepa — it says what buyers picked, not what a maker claims.
Specifications: the manufacturer sheet for home security products and the matching Amazon product page. Prices and availability: Keepa. Every figure on this page names its source.
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.
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
