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BRAND:  yolink        MODEL: YS7904-uc  

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YoLink LoRa 1/4 Mile Long Range Water Level Monitoring Sensor, Alexa and IFTTT. YoLink Hub Required - YoLink
YoLink LoRa 1/4 Mile Long Range Water Level Monitoring Sensor, Alexa and IFTTT. YoLink Hub Required - YoLink


Probe cable style water leak sensor for the monitoring of water levels, with integral sounder. Alexa, IFTTT, and Home Assistant-compatible. Please note: a YoLink Hub or SpeakerHub is required (see below).




Free U.S. Shipping, Orders $50 & Up

Hassle-Free 60 Day Returns

2-Year Warranty

Do-It-Yourself Installation

U.S. Phone Support Available

100% Satisfaction Goal




Home Assistant

Raedius Web Console


  • Smart water detector with a built-in siren, detects the presence or absence of water and displays the status on the YoLink app
  • This product is a variant of the Water Leak Sensor 2 and 3. Both products are the same sensor, but settings in the YoLink app determine if this sensor acts as a water leak detector or a water level monitoring sensor
  • The sensor body is compatible with most float switches, which may be preferred for some applications (see the Applications section, below)


  • Exceptional value; high-quality wireless smart water level monitoring at a great price
  • Be informed immediately of low water levels such as low water level in a fish tank
  • Create custom automation using the YoLink app, to trigger responses from other YoLink devices, such as the Siren Alarm
  • Compact design and wired probe allows for placing the sensor where others may not fit
  • Easy to install and portable; move to other locations as needed
  • Lower cost of ownership than other technologies; low-power operation means batteries may last over 2 years, compared to 1 or less from other brands
  • Carefree maintenance, with more years between battery replacement
  • Low-battery alerts give you advanced warning that it is almost time to replace the batteries
  • Uses standard alkaline batteries (2 AAA batteries); no Lithium or special batteries required
  • Works with the convenient and user-friendly YoLink app
  • Extremely easy and fast installation using the YoLink app with Scan & Play


  • Be alerted when the swimming pool water needs to be topped-off
  • Be alerted to fish tank water leaks immediately
  • Manage the water levels in storage or other liquid tanks

  • Water level detection applications include monitoring water levels in water supplies, such as those used for fish tanks, pets, livestock, plants, gardening, horticulture, and agriculture
  • Toilet applications: runaway toilet (internal leak or flapper jamb), flush monitoring, exhaust fan automation
  • Humidifier and dehumidifier water tank monitoring
  • YoLink’s industry-leading long range communication allows for placing the sensor in separate garage buildings, sheds, storage buildings, barns, greenhouses, etc.
  • For some applications we recommend using our sensor with a float switch, rather than with the included probe cable. For saltwater applications, such as a bilge tank in a boat, or for use with hard water, or water or other liquids that are not clean, build-up on the electrodes can occur that can lead to inconsistent or delayed responses from the sensor. To avoid this, and for years of trouble-free operation, we suggest connecting the sensor to a non-powered float switch. The float switch must have "dry" (no power) contacts, and they can be normally-open or -closed (many float switches have selectable outputs), but ideally have normally-closed output/contacts for high level (liquid detected) and open contacts for low level (no liquid detected). Simply cut the probe end of the cable off, and splice the two conductors to the float switch conductors. Alternatively, the entire cable can be replaced with one appropriate for your application (longer length, outdoor rated, etc.), but the cable must have a standard 3.5 mm headphones style male connector, to be plugged into the Water Level Monitoring Sensor. Wire splices should be made with waterproof type wire connecting methods, if they are to be submerged or subjected to rain, etc. 
  • Semtech® LoRa® RF Module YL09 microcontroller with 32-Bit RISC processor
  • Color: White
  • Set button (Front)
  • Power: 2 AAA batteries (3V DC)
  • Dimension [L x W x D]: 2.44 x 2.44 x 0.80 inches (83.06 x 30.99 x 14.99 mm)
  • Environmental:
  • Operating Temperature Range: -4°F – 122°F (-20°C – 50°C)
  • Operating Humidity Range: ≤95%RH non-condensing
  • Intended for indoor use only
  • (1) YoLink Water Level Monitoring Sensor (aka Water Leak Sensor 2) (batteries included)
  • (1) Probe Cable
  • (1) Mounting Hook
  • (1) Quick Start Guide
  • YoLink Hub with an internet connection (wired Ethernet or 2.4GHz Wi-Fi). Refer to the Hub user guide for additional information
  • Smartphone or tablet running iOS 9 or higher, Android 4.4 or higher
  • Tools Required: None
  • Installation Difficulty Level: Super Easy
For full functionality, including for the app to work, YoLink devices must connect to at least one hub (YoLink Hub or SpeakerHub), and that hub must have an internet connection. Unless you are adding devices to an existing YoLink account, or unless your building is covered by an existing YoLink or Raedius wireless network, please add one hub to your order.

Automatic water shut-off is an important part of a comprehensive water leak protection system. Consider adding a Bulldog Valve Robot or a Motorized Valve and Smart Wireless Valve Controller to your YoLink system. Learn more here

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Wireless Smart Water Valve Controller, with Bulldog Valve Robot HUB REQUIRED - YoLink
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YoLink LoRa 1/4 Mile Long Range Smart Water Leak Sensor, EASY Installation, Alexa, IFTTT.  Hub Required - YoLink
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YoLink Water Leak Sensor 2
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YoLink Water Leak Sensor 3

Q: Can I adjust the volume of the siren?  A: No, but you can disable it (turn it off entirely in the app). Consider our SpeakerHub, for a lot more options on sound level and type. 
Q: Can I not use this product outdoors?  A: The sensor body is designed for indoor use. You may use it for outdoor applications as long as the sensor remains within the temperature and humidity range listed in the specifications, above. The sensor body can, for example, be installed in a protective enclosure (the sensor body should not get wet).
This product is a member of the following collections:

Water Sensors Collection

Smart Aquarium

Smart Water Solutions Collection

Do you have questions? We have answers!

Do you have questions? We have answers!

Please fill out the form below, or if your matter is urgent, please call us at  949-825-5958. Please note our Irvine, California office hours: 9AM - 5PM Pacific, Monday through Friday. You may experience waits as we attend to previous customer requests. 

Please fill out the form below, or if your matter is urgent, please call us at  949-825-5958. Please note our Irvine, California office hours: 9AM - 5PM Pacific, Monday through Friday. You may experience waits as we attend to previous customer requests.