WS303 vs EM300-SLD vs EM300-ZLD: Milesight Leak Detection Sensors Compared
Short answer: the WS303 (£41.90 ex VAT) is the cheap, small unit you scatter under appliances, sinks and boilers. The EM300-SLD (£53.87) is the same job in an IP67 housing with a proper probe — for plant rooms, voids and anywhere damp or dirty. The EM300-ZLD (£71.82) swaps the probe for a sensing cable, so one device watches a whole run — pipe corridors, server-room perimeters, riser cupboards, tank bunds.
All three are LoRaWAN, battery-powered for years, and alarm the moment water bridges the sensing element — into email, SMS or your BMS via a UG63 or UG65 gateway. No wiring at the leak point is the entire reason these get installed where wired leak detection never did.
The comparison
| Model | Price (ex VAT) | Detects via | Coverage | Fit it… |
|---|---|---|---|---|
| WS303 | £41.90 | Contact probes on the base | One spot | Under sinks, dishwashers, boilers, AC drip trays |
| EM300-SLD | £53.87 | External spot probe, IP67 body | One spot, harsh locations | Plant rooms, ceiling voids, external meters, pits |
| EM300-ZLD | £71.82 | Water-sensing cable | A whole run per device | Server rooms, risers, pipe corridors, tank bunds |
Spot or zone? The one decision that matters
A spot sensor only alarms when water reaches that point, so the craft is in placement: the lowest point, the drip line, the first place water pools. Where water could surface anywhere along a run — a pipe corridor, the perimeter of a server room floor — a zone cable is the honest answer, because guessing the pooling point is how leaks get found by the ceiling below instead.
Deployment notes from real installs
- Insurance-driven jobs: escape-of-water is the biggest claims line in UK commercial property. A floor of spot sensors plus zone cable in risers is the pattern insurers’ risk engineers ask for — see our guide to the six zones that stop costly claims.
- Batteries: years at default intervals; alarms transmit immediately regardless of the reporting schedule.
- Test them: a wet finger across the probes on install day proves the whole chain — sensor, gateway, alert route — while everyone is still on site.
- One gateway covers the building: leak sensors, temperature sensors and anything else LoRaWAN share it.
All three sensors are UK-stocked with published pricing. Get a trade quote or call 023 9223 3611.
The short answer
Which Milesight leak detection sensor should I fit?
Use the WS303 (£41.90 ex VAT) as the cheap spot sensor under appliances, sinks and boilers. Use the EM300-SLD (£53.87) where it is damp, dirty or outdoors — same job, IP67 housing and a proper probe. Use the EM300-ZLD (£71.82) where water could surface anywhere along a run: its sensing cable covers server-room perimeters, risers, pipe corridors and tank bunds with one device.
Frequently asked questions
Do leak sensors need Wi-Fi?
No. They talk LoRaWAN to a gateway, which then uses Ethernet, Wi-Fi or 4G. That is why they work in basements and risers where Wi-Fi does not reach.
How fast is a leak alert?
Leak events transmit immediately — typically seconds from water contact to notification, regardless of the routine reporting interval.
Can the EM300-ZLD sensing cable be extended?
Yes, the water-sensing cable is extendable. Tell us the run length when you request a quote and we will specify it.
Spot sensor or zone cable?
A spot sensor only alarms when water reaches that exact point, so placement is everything. Where water could pool anywhere along a run, a zone cable is the honest answer — guessing the pooling point is how leaks get found by the ceiling below instead.
How long do the batteries last?
Years at default reporting intervals. Alarm transmissions happen immediately and independently of the reporting schedule.
Related
Buying this in the UK
- Supplied by Indiott, a trading name of PSI Technologies Limited (Companies House 03689664, VAT GB 730 2340 83), Hampshire, United Kingdom.
- Every price is published ex VAT at indiott.com — no quote needed to see it.
- Typically dispatched within 14 working days from the UK, on a VAT invoice.
- Call 023 9223 3611 or request a quote.
Next step
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