Before the rounds: why these three?
There are twelve cellular boat monitoring systems currently shipping that we track on SmartBoats.org. We wrote a full buyer's guide that surveys them all. This guide does something different: it takes the three most-recommended systems in forum discussions — the ones you'll actually be choosing between after an evening of research — and walks through the specific trade-offs head-to-head.
Why these three and not Garmin OnDeck or BRNKL or Nautic Alert? A few reasons. Garmin OnDeck is primarily an accessory to a Garmin helm — the decision about whether to buy it is really the decision about whether you're a Garmin ecosystem boat. BRNKL and Boat Command are real products but have niche positioning (camera-first and predictive-maintenance-first respectively). Nautic Alert is a premium segment entirely — at $2,700 over three years it's not competing with the others on price.
Siren, ArmIt, and Yacht Sentinel are the three systems that come up when a boater posts "I'm shopping for a cellular monitor — what should I buy?" on a forum and asks for real recommendations. So this guide is written around that specific decision.
We scored each system across ten criteria, awarded a round winner based on the evidence, and summed the rounds at the end. Where a tie is legitimate, we called it a tie. Where one system is clearly best, we said so — and explained why.
ArmIt BilgeMAX One kit: $229.99. Siren 3: $299.99, plus $139.09 per wireless sensor. Siren 3 Pro: $799.99. Yacht Sentinel YS Pro: €1,590 excluding VAT, plus €60–€130 per wireless sensor.
ArmIt wins because there's no hub — each battery-powered MAX device connects to ArmIt's network on its own, so you pay for exactly what you need. The catch is coverage: ArmIt only works where its private network reaches. Round 2 and Round 3 cover that.
Headline hardware price is a poor guide to what you'll actually pay. Service subscriptions compound. Here's the real 3-year total for each system in three realistic scenarios:
| Scenario | Siren 3 / 3 Pro | ArmIt | Yacht Sentinel YS Pro |
|---|---|---|---|
| Just bilge monitoring (1 sensor, basic) | $1,114 (Siren 3 + high-water sensor) | ~$530 (BilgeMAX One, Sentinel plan) | ~€2,430 (YS Pro + bilge sensor) |
| Comprehensive coverage (bilge + battery + hatch/intrusion) | $1,392 (Siren 3 + 3 sensors) | ~$999–$1,374 ($549 kit + $150–$275/yr plan) | ~€2,510 (YS Pro + 2 sensors; battery voltage built in) |
| Full integration (NMEA 2000 + engine data) | $975 (Siren 3) / $1,475 (Siren 3 Pro), plus sensors | Not possible | ~€2,310 (YS Pro), plus sensors |
Siren totals use the $225 annual plan (Siren's $575 three-year plan trims about $100); Yacht Sentinel totals use the €20/month EU/US rate and exclude VAT. ArmIt is cheapest for sensor-only monitoring — if its network covers your boat. Siren is cheapest once you want NMEA 2000 engine data, and one subscription covers every sensor you add. Yacht Sentinel is the most expensive of the three; you pay for its multi-country coverage and built-in data features.
The three no longer share a network model. Siren's main devices use global LTE cellular (4G/5G LTE-M on the Siren 3), and the Siren 3 Pro can add SirenSat, a Globalstar satellite antenna ($259.99 plus $350/yr on top of the cellular plan) that tracks position and geofences outside cellular range. Yacht Sentinel's YS Pro has an embedded 3G/4G SIM with published coverage zones spanning more than 100 countries (€20/month in the EU and US zones, €25–€50 elsewhere), keeps logging when out of range, and can also use your own SIM, Wi-Fi or Ethernet. ArmIt has left cellular entirely: its sensors run on its private EarthSmart Maritime Network, which covers specific marinas and waterways, and ArmIt checks coverage location by location. Its Voyager add-on ($199 provisioning plus $149.99/yr) keeps the sensors connected when you leave that coverage, through onboard internet such as Starlink or roaming carrier networks (standard plan: North America, US territories, European waterways, Australia, the Bahamas and Bermuda); ArmIt also says it can fall back to satellite, without naming the network.
For a US boat, Siren's coverage is the simplest, and SirenSat is the only satellite option of the three with published pricing — though it is position tracking, not bilge alerts. For a boat based in Europe or moving between countries, Yacht Sentinel's published multi-country coverage is the most transparent. None has a built-in satellite link for sensor alerts; YS Pro and ArmIt's Voyager can ride an onboard connection such as Starlink. For ocean passages without one, add a satellite communicator.
Yacht Sentinel wins this round for international sailors; Siren wins for US boats. ArmIt is only as good as its coverage map at your marina.
Siren and Yacht Sentinel both build NMEA 2000 in. Siren lists built-in NMEA 2000 and Yamaha Command Link connectivity on the standard Siren 3 (the connection cable kit is $38.47 extra), and the Siren 3 Pro adds more wired inputs and outputs plus digital-switching integration; Siren says both track engine performance. Yacht Sentinel's YS Pro reads NMEA 2000 plus J1939, CAN and Modbus data, and has a relay that powers up the boat's NMEA 2000 network on request from the app to refresh readings.
ArmIt has no NMEA 2000 support whatsoever. The sensors are standalone and don't talk to your boat's data backbone.
If your boat has NMEA 2000 and you want to monitor engine data, Siren is the cheaper way in and Yacht Sentinel reads more bus types. If your boat is a sailboat or small powerboat without a modern backbone, this round doesn't matter and you can ignore it.
Siren's Siren 3 Series wireless sensors cover battery, bilge-pump activity, entry/hatch, high water and temperature ($139.09 each, on a battery rated for two years), plus wired security switches, canvas-snap and reed switches, a shore-power sensor plug and relays. Every sensor appears in the same dashboard.
Yacht Sentinel's YS Pro accessory range is at least as broad: bilge (with or without a probe), entry, motion, smoke, heat, air quality, humidity, shore power, a voltage detector, a key fob and a Zigbee range extender, mostly €60–€130 each. ArmIt's MAX series is narrower but no longer bilge-only: BilgeMAX One, battery, motion, a general access/temperature/dry-contact node, shore-power and generator monitoring.
Siren and Yacht Sentinel tie: both are hub-based platforms where the next sensor is a small add-on. ArmIt now prices by plan tier rather than per sensor — up to three MAX devices on the $150/yr Guardian plan, unlimited on the $275/yr Command plan — so growing an ArmIt install no longer means a new plan per sensor, but the catalog is thinner.
The Siren Connected Boat app is, by a meaningful margin, the best app in this category. It's been through multiple major redesigns, ships on a reliable update cadence, has genuinely thoughtful UX (one-tap system-check, configurable alert severities, organized history view) and — most importantly — notifications arrive reliably and quickly. Forum consensus across Hull Truth, Cruisers Forum, and Sailboat Owners is consistent on this.
Yacht Sentinel's YS Pro app launched with the YS Pro in 2023, alongside a free "Partner Platform" for dealers and charter fleets. It covers live and historical data, alarms and maintenance; we haven't seen enough of it to rank it above Siren's.
ArmIt's myARMIT portal is the thinnest of the three — built around alert history and device check-ins rather than a dashboard of boat systems.
ArmIt is the easiest install in the category. MAX devices are wire-free and battery-powered, with no hub and no pairing step: place the BilgeMAX float and sensor, activate it, done. No wiring to boat power, no shore power connection. (ArmIt says larger multi-device setups may be better left to a dealer.)
Siren 3 (standard) is a moderate install — you need to find 12V DC power for the hub and mount the wireless sensors. Most owners can do it in two to three hours. The Siren 3 Pro benefits from professional installation because of its NMEA 2000 integration.
Yacht Sentinel is middle ground. The company says a YS Pro retrofit takes under 30 minutes, with NMEA 2000 data detected automatically, but you still need to find power and mount the 4G/GPS antenna and any sensors — closer to Siren 3 in practice.
Siren publishes the Siren 3 Pro's draw as under 20mA at 12V while asleep on the network and 70mA while actively tracking — roughly 0.5 to 1.7Ah a day. For a boat with shore power, this is a rounding error. For a mooring-field boat on a modest battery bank, it's enough that you'll need to think about it.
Yacht Sentinel quotes under 0.3 W for the YS Pro while the boat is idle — about 25mA at 12V.
ArmIt sensors draw nothing from the boat. MAX devices run for years on their own internal batteries. On a mooring-field boat with no shore power, this is transformative.
This matters more than people realize when buying a $500–$1,500 system that's supposed to last ten years. If the vendor folds, the cloud service folds with it, and you have a $1,000 paperweight.
Siren wins on corporate durability — Yamaha acquired Siren in 2021 and now ships Siren 3 hardware factory-installed on 29-foot Yamaha sport boats. Yamaha is a Fortune 500 company with a century-plus history in marine.
Yacht Sentinel is privately held, has built connected-boat hardware since 2008, and bought TSM Systems (Tow Pro) in January 2025. We consider them durable but would be less surprised to see them acquired than Siren. ArmIt is a smaller independent that has just rebuilt its product line around its own private network — the product is good but the company is the most exposed to risk of the three.
None of these three have a genuine off-ramp. None export data via Signal K. None offer a raw-data API you can use to build dashboards in Home Assistant or Grafana. None have a documented "what happens if this vendor shuts down" plan.
This is the single biggest systemic weakness in the cellular-monitor category. If your boat's data matters to you over a decade, all three represent a bet on vendor viability. The open-source alternative (Signal K + SensESP + cellular modem) is the only genuinely portable option, and it's a different product with different trade-offs.
We'd pay a meaningful premium for a cellular monitor with a documented data-export feature. As of April 2026, that product does not exist.
The scoreboard
Ten rounds, tallied:
| Round | Winner |
|---|---|
| 01 · Hardware price | ArmIt |
| 02 · 3-year total cost | Depends — sensors only: ArmIt (where covered); NMEA 2000 data: Siren |
| 03 · Network & coverage | Yacht Sentinel (intl); Siren (US) |
| 04 · NMEA 2000 integration | Tie — Siren and Yacht Sentinel |
| 05 · Sensor ecosystem depth | Tie — Siren and Yacht Sentinel |
| 06 · App quality | Siren |
| 07 · Installation difficulty | ArmIt |
| 08 · Power consumption | ArmIt |
| 09 · Vendor durability | Siren |
| 10 · Data portability | Tie (all fail) |
Tally: Siren wins two rounds outright (app and vendor durability), splits coverage, and shares NMEA 2000 and sensor ecosystem with Yacht Sentinel. ArmIt wins three rounds on hardware, install, and power, and is cheapest on three-year cost wherever its network reaches. Yacht Sentinel wins coverage for international boats. Each system wins the right rounds for a different kind of buyer — the rounds that matter to you depend on your boat and usage.
Which one should you actually buy?
Frequently asked questions
Does your boat have shore power or reliable solar, and will you monitor more than two things?
Yes — buy a Siren. The platform economics, app quality, and vendor durability make it the right answer. Pick the Pro if you want digital switching, more wired inputs, or the SirenSat satellite-tracking option; pick the standard Siren 3 otherwise (it already has NMEA 2000 built in).
Is your boat on a mooring without shore power, or a trailer-sailor that spends most of its life on land, and do you just need bilge alerting?
Yes — buy ArmIt, if its EarthSmart network covers your mooring or storage spot (ArmIt checks each location). The no-hub, no-boat-power model is genuinely the right tool. A BilgeMAX One kit ($229.99) on the $100/yr Sentinel plan is about $530 over three years; adding battery or shore-power devices moves you to the $150/yr Guardian plan, which covers up to three devices.
Does your boat cruise internationally, visit destinations with patchy cellular, or spend time in Mediterranean waters?
Yes — look hardest at Yacht Sentinel's YS Pro. It has an embedded 3G/4G SIM with published coverage in more than 100 countries and keeps logging when out of range. None of the three has a built-in satellite link for sensor alerts: Siren 3 Pro's SirenSat add-on tracks position only, ArmIt says its Voyager add-on can fall back to satellite without saying which network, and YS Pro can use the boat's own Wi-Fi or Ethernet (such as Starlink). For ocean passages without onboard internet, add a satellite communicator.
Is Siren Marine owned by Yamaha?
Yes. Yamaha acquired Siren Marine in 2021 and now ships Siren 3 hardware factory-installed on 29-foot Yamaha sport boats. That corporate backing is the main reason Siren wins our vendor-durability round.
Can I export my data from Siren, ArmIt, or Yacht Sentinel?
No. As of April 2026, none of the three systems export data via Signal K or offer a documented raw-data API. This is the single biggest systemic weakness of the cellular-monitor category. If portability matters, the open-source Signal K + SensESP + cellular modem stack is the only genuinely portable answer.
The short version
Siren has the best app and the most durable corporate parent, and shares the NMEA 2000 and sensor-ecosystem rounds with Yacht Sentinel. ArmIt wins on simplicity and low-power install, which matters enormously for a specific kind of boat (mooring-field, no shore power, minimal monitoring needs) — where its network reaches. Yacht Sentinel wins on international cellular coverage and matches Siren on NMEA 2000 data, which matters for European and international cruisers; none has a built-in satellite alert link for mid-ocean. Match the system to your use case — not the other way around.
What we'd change our minds about
We'd reconsider this head-to-head if:
- ArmIt's EarthSmart network grew to the point that coverage stops being the first question. Its tiered plans already make multi-sensor setups cheap; coverage is what holds it back.
- Yacht Sentinel significantly expanded its North American dealer network, making installation and support comparable to Siren's.
- Any of the three shipped a Signal K export feature or documented raw-data API.
- Siren changed its subscription pricing substantially — a 30% reduction in the annual plan would make Siren the clear winner in more scenarios.