Blue Sea Systems M2 OLED Temperature Monitor, 7-70V DC, Up to 4 Sensors, -40°C to 120°C

Overview

The Blue Sea Systems 1841 is a panel-mounted OLED temperature monitor for tracking up to four temperature points on board. It runs on 7 to 70V DC, reads from -40°C to 120°C (-40°F to 250°F), and shows data on a 55 mm x 28 mm display with Fahrenheit or Celsius readout.

This is a practical fit for boats that need local temperature data and alarms without relying on a multifunction display. It works well for engine exhaust monitoring and other onboard temperature checks where a dedicated readout at the helm, switch panel, or machinery space is easier to use. The unit also includes an 80 dB audible alarm and a 500 mA isolated MOSFET relay output for an external alarm or relay-triggered circuit.

Key features

• Monitors up to four temperature sensors from a single display
• 7 to 70V DC input range suits 12V and 24V systems and other higher-voltage DC installations
• Temperature range from -40°C to 120°C (-40°F to 250°F)
• Auto-dimming OLED display with a 55 mm x 28 mm viewing area
• Adjustable high and low temperature alarms with an 80 dB audible alert
• Isolated 500 mA MOSFET relay output for external alarm or relay-based control
• ABYC compliant for engine exhaust monitoring
• Surface, flat-panel, and 360 panel mounting options
• Unit face is IP66 when surface-mounted as directed

Compatibility and fit

This monitor is a strong match for refit and new-build installations where temperature needs to be watched in more than one place. On many boats that means exhaust temperature, engine room hot spots, refrigeration spaces, or other equipment areas where a local alarm matters more than network integration.

Mounting location matters. The face is IP66 only when the unit is surface-mounted according to the installation guidance, so that setup makes the most sense in exposed helm or cockpit panels. Flat-panel and 360 panel mounting are better kept in protected locations because the rear of the meter is not waterproof. The standard surface-mount cutout is 2.125 in (54 mm).

Installation and setup

The included sensor mix gives flexibility for different onboard locations, with submersible sensors for wet areas and high-temperature sensors for hotter points in the system. When using multiple sensors, keeping their negative leads terminated close to the meter's pin 1 helps avoid reading errors.

The relay output is useful when you want the monitor to do more than display data. It can trigger an external alarm or switch an external relay when a channel crosses a set threshold. That makes it a good fit for skippers and installers who want dedicated temperature monitoring with local warning capability at the panel.

What’s included

• M2 head unit
• Surface-mount bezel and cover
• Flat-mount bezel and clamp
• Mounting ring and mounting nut
• Surface-mount gasket and seal
• Connector and screwdriver
• Two submersible temperature sensors
• Two high-temperature sensors
• Mounting screws

Orders are processed within 2 business days, which includes verification, packing, and dispatch. Orders of $100 or more qualify for free shipping when eligible. For orders under $100, shipping costs are calculated at checkout based on destination, package weight, and selected service. International shipping is available for eligible products, and certain items may require additional handling, warehouse transfers, or may ship directly from the manufacturer, which can affect processing time.

Deliveries are handled by preferred carriers such as USPS, UPS, FedEx, DHL, and others depending on your location and selected service. Estimated delivery times are displayed at checkout and may vary due to customs processing, carrier delays, weather, postal disruptions, or other circumstances beyond our control. Once your order ships, you'll receive a confirmation email with tracking information. Tracking may take up to 24 hours to update on the carrier's website and is also available through your account when applicable.

We ship throughout the United States and to most international destinations for products eligible for international shipping. International orders may be subject to customs duties, taxes, brokerage charges, or other import fees, which are the customer's responsibility and are not included in the product or shipping price. PO Boxes are accepted only when shipping through USPS, and not all packages qualify for this option. If your order does not arrive within the estimated delivery window, please contact us at info@apollolighting.com or +1 (954) 375-0100 so we can assist with locating your package.

Learn more.

Returns may be requested within 30 days of receiving your order. Items must be unused, uninstalled, unaltered, and returned in their original packaging with all tags, packing materials, blank warranty cards, manuals, instructions, accessories, and included items. Certain products, including installed or used electronics, electrical components, lighting, consumables, custom or special-order items, cut-to-length products, safety equipment, and merchandise exposed to water or marine conditions, may not be eligible for return.

To request a return, sign in to your account and select the applicable order and items, and submit your request for review. Eligible unfulfilled items may also be submitted for cancellation within 1 hour of placing the order. Returns or cancellations are not considered approved until you receive confirmation from Apollo Lighting. Please do not ship or drop off merchandise before receiving return approval and instructions.

Customers are responsible for arranging and paying for return shipping unless the return is due to an error by Apollo Lighting or the item is verified as defective, damaged, or incorrect. Missing, damaged, defective, or incorrect items must be reported within 2 business days of delivery, and photos or other documentation may be required for review. If the issue is verified, Apollo Lighting may provide or reimburse return shipping and issue a replacement or refund depending on the circumstances. International customers are responsible for return shipping, duties, taxes, customs charges, brokerage fees, and other costs associated with an international return.

After your return is received and inspected, approved refunds are issued to the original payment method and may take 5-7 business days to appear after processing. Original shipping and handling charges are nonrefundable, and the value of any included free items that are not returned may be deducted from the refund. Apollo Lighting does not charge a standard restocking fee on eligible returns. Returns that are incomplete, damaged, installed, used, altered, improperly packaged, or otherwise do not meet the eligibility requirements may be refused. We recommend using a trackable and appropriately insured shipping service for all customer-arranged returns.

For assistance, contact info@apollolighting.com or call +1 (954) 375-0100.

Learn more.

Many products sold by Apollo Lighting include a manufacturer's warranty covering defects in materials or workmanship. Warranty terms vary by brand, product category, and model, so eligibility, coverage duration, exclusions, and available remedies are determined by the applicable manufacturer. We recommend reviewing the warranty information provided with your product before installation or use, especially for marine electronics, navigation equipment, lighting, electrical systems, pumps, safety equipment, and other specialized marine products.

If you need warranty service, the claim must follow the process established by the manufacturer, authorized service center, or designated warranty provider. You may be asked for proof of purchase, a serial number, product registration, photos, maintenance or installation records, or other documentation. Apollo Lighting does not determine or modify a manufacturer's warranty coverage or final claim decision, but we are happy to help provide purchase information and direct you to the appropriate manufacturer or warranty resource.

Keep your receipt, product documentation, serial number information, and original packaging when practical. Damage caused by normal wear, misuse, improper installation, insufficient maintenance, corrosion, impact, unauthorized modifications, electrical issues, or operation outside the manufacturer's specifications may not be covered. Warranty claims are separate from standard returns, so a product that has been installed, used, or exposed to marine conditions may no longer qualify for return while still remaining eligible for evaluation under the manufacturer's applicable warranty.

Learn more.