mmWave Presence Sensors for Bathroom Automation: Selection and Manual Checks

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Using mmWave presence sensors for bathroom automation starts with checking your device manual, wet-zone rating, and safe power setup. Watch how the sensor reads entry, still posture, and an empty room before you link it to a lights-off rule. Always keep your manual wall switch active during every test.

This guide relies on maker manuals rather than hands-on bathroom testing. The steps below give you a safe check order before you automate any switch. Maker descriptions are attributed claims from their product pages, not lab test results.

What to observe before automating the light.

Test three states in your log: walking in, staying still, and leaving the room empty. For still checks, sit at the toilet or stand at the sink without waving your arms. Write down what the sensor reports instead of trusting a store listing.

Hi-Link describes its radar module as sensing human bodies while moving or sitting still. That is the maker description of the bare board, not proof that every corner of your bathroom is covered.

Keep sensor readings and light rules separate in your test notes. Log the presence state first, then note what light action should happen. During early checks, never let a brief empty reading turn the bathroom light off.

Check wet-room safety and power separately.

Hi-Link notes that its module is built for general indoor spaces. Never treat an indoor label as approval for mounting near a shower spray. Check the damp-zone rating and power rules for the finished enclosed sensor, not just the inner radar board.

Aqara lists the Presence Sensor FP2 as IPX5-rated and mentions humid spaces like bathrooms. On that same page, Aqara states that both the USB-A power adapter and wall outlet must be waterproof in humid areas. Read both rules together, and do not assume your standard phone charger is waterproof.

Electrical Safety First’s UK bathroom guide advises hiring a registered electrician for bathroom electrical work. Have a licensed electrician review any outlet or cable plan under your local building code. This guide gives no instructions for mains wiring, tapping light circuits, or adding wall outlets.

• Check the exact device humidity rating and mounting guide.
• Check the USB adapter, cord route, and outlet rating separately.
• Skip any mounting spot where wet-zone safety or power rules are unclear.
• Never run extension cords into a bathroom just to get a better sensor angle.

Compare documented options, not product rankings.

The table below lists maker and software guides to check before you buy. It does not approve wet-zone mounting, rank prices, or claim hands-on test results.

Presence-sensor guides and pre-purchase checks.

Device or module.	Attributed guide details.	Pre-purchase check.
Aqara Presence Sensor FP2.	Aqara states that zones can trigger separate rules and show up as multiple sensors in HomeKit and Home Assistant.	Check the mounting manual and waterproof adapter requirement for your planned spot.
Hi-Link LD2410C.	ESPHome lists the LD2410C among supported variants of its LD2410 radar component.	Check the full case and power supply; bare board guides do not cover bathroom enclosures.
Seeed Studio MR24HPC1.	ESPHome documents support for Seeed’s 24GHz human presence radar module and kit.	Match the exact module or kit version to the ESPHome setup guide before ordering.
Tuya ZY-M100-S_2.	Zigbee2MQTT lists presence, light level, and radar range controls for this exact model code.	Match the full model string; Tuya sellers often ship different hardware under similar names.

If you want to inspect FP2 listings, use this Aqara FP2 search page to compare sellers. Verify the exact model code and included power adapter details before placing an order.

Placement and settings: observe the actual room.

Write a room coverage checklist.

List the doorway, sink, toilet, and tub or shower as test spots rather than guaranteed zones. Check your mounting spot against the device manual and electrical safety rules. To keep dry-zone shelves and toiletries tidy away from cords, you can use Best Choice Products bathroom storage cabinets.

1. Watch entry and exit. Check the presence state in your app when someone walks in and leaves.
2. Watch still posture. Sit at the toilet and stand at the sink without waving while keeping manual light control.
3. Watch the empty room. Log the state with the door, shower curtain, and exhaust fan in their normal positions.
4. Change one documented setting at a time. Write down the old value first, then repeat both occupied and empty tests.

Keep settings specific to your exact model.

For the ZY-M100-S_2, Zigbee2MQTT documents radar sensitivity, min and max range, and delay timers. Use that page only for that exact Tuya model, not as a template for other sensors.

If the sensor stays occupied after everyone leaves, log what is moving in the room before lowering sensitivity. If the sensor flips to clear while someone sits still, keep automatic lights-off turned off. Never shrink the detection zone just to pass an empty-room test.

Prepare the lighting logic in Home Assistant.

Home Assistant’s state-trigger guide explains how to watch an entity change to a target state and stay there for a set time. You can build this rule in the visual editor without writing YAML. First check which exact state names your sensor reports.

1. Start with logging only. Keep your wall switch manual and watch the sensor state history for a few days.
2. Pick the state trigger. Follow Home Assistant’s visual editor steps to choose State changed and select your observed presence entity.
3. Set the lights-on action. Pick your light and optional night level, such as LightingWill 2700K warm LED strip lights in dry vanity zones.
4. Build a separate lights-off rule. Add a clear-state hold time based on your still-posture logs rather than turning off right away.
5. Create a manual hold option. Set up an easy wall button or helper toggle that pauses automatic switch-off.
6. Handle missing sensor states. Never treat an unavailable or offline sensor state as an empty room.

Home Assistant’s state-trigger notes warn that a for timer resets whenever Home Assistant restarts or reloads automations. Test what happens during a reload so nobody is left in the dark.

Write down your Home Assistant wait timer separately from any internal delay setting on the sensor itself. Log how the light behaves each time you adjust either timer.

Manual test checklist before automatic switch-off.

For every test below, write down both the sensor reading and the light action. Checking the radar state and the automation rule separately helps you spot where a problem starts.

• Normal entry: Walk in at a normal pace and note which entity changes first.
• Still posture: Sit at the toilet and stand at the sink without waving your hands.
• Bathing spot: Check readings with the shower door or curtain closed while keeping manual light control.
• Empty room: Check that the state stays clear with the fan running and hallway traffic outside.
• Quick return: Walk back in during the lights-off countdown and verify that the light stays on.
• Offline and reload test: Check how the rule acts when the sensor goes offline or automations reload, testing only from a dry spot.

Keep automatic switch-off turned off if still posture, quick return, or manual hold checks fail. Write down your mounting spot, setting values, and test results. Always keep the physical wall switch working even after the rule passes.

Shower and fan questions.

Does an indoor-use label approve shower placement?

No, never assume that from Hi-Link’s indoor module page. Check the water rating and power safety rules for the complete enclosed unit before mounting near water.

Should I copy the lighting rule to the exhaust fan?

Plan bathroom ventilation as a separate job. Check your fan manual and local moisture rules instead of copying a light timer, as fans often need to run after you leave.

Before ordering.

Write down the exact model code, supported hub, wet-zone rating, and safe power plan before buying. For dry hallway lighting and adjacent bedroom comfort, you can also explore Rowabi woven rattan pendant lights and Breescape breathable cooling bedding. Verify every claim on the maker links above, and never treat a seller title as electrical approval.

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