The Extech SL400 is a compact, lightweight personal noise dosimeter with a USB interface designed to test noise exposure and provide noise surveys for compliance with OSHA, MSHA, DOD, ACGIH, and ISO standards. It includes PC software to control setup and retrieve stored events or analyze real-time measurements, supporting the workflow of safety professionals who need to document worker sound exposure across an 8-hour shift.

Listed applications include personal accumulated noise exposure measurement, workplace noise assessment, and OSHA and other regulatory agency compliance work. For employees exposed to loud noise, sound level monitoring is essential to determine what protective measures are required, and the SL400 supports both OSHA and IEC noise accumulation surveys to determine total sound exposure over an 8-hour period.

Brand Heritage

Extech Instruments is owned by FLIR Systems, which itself became part of Teledyne Technologies in 2021. The Extech brand continues to operate as a recognized name in handheld environmental and safety test instruments, with the FLIR Systems copyright still appearing on current product documentation.

Compare Other Models in This Series

The SL400 is positioned in the Extech catalog as a personal noise dosimeter — a body-worn instrument designed to accumulate a worker's total sound exposure across a shift rather than to take a single spot reading of a noise source. The clip-on 0.5 inch microphone on a 32 inch cable is the architectural signature of this category: the microphone sits at the worker's shoulder near the hearing zone while the instrument body clips to a belt.

Within Extech's sound measurement line, dosimeters and sound level meters serve different jobs. A dosimeter like the SL400 answers the question of how much cumulative noise a specific worker received over a shift, while a handheld sound level meter answers the question of how loud a specific location or machine is at a specific moment. Both categories share underlying acoustic measurement technology but differ in form factor, datalogging behavior, and the regulatory frameworks they are typically used to satisfy.

Each new SL400 listed in our catalog is its own dedicated product page with condition-matched pricing and availability. If you are comparing options across condition tiers, the individual product pages carry the specifics relevant to your purchasing process.

The SL400 is specifically called out as available with optional Limited NIST traceability for A and C weighting, ordered with the -NISTL suffix to receive the product plus a calibration certificate. This is the relevant ordering detail for buyers whose internal procedures or external audits require documented traceability on the weightings used for occupational noise measurement.

Comparison across condition tiers and ordering variants for the SL400 centers on two factors documented on the datasheet: whether the unit is ordered with the standard SL400 part number or with the -NISTL suffix for Limited NIST traceable calibration on A and C weighting, and whether the optional 94 dB calibrator is included to support the before and after calibration checks referenced in the specifications.

Specifications themselves — measurement range, frequency weighting, response rates, memory depth, measurement modes, and the standards compliance list — are common to the SL400 platform as printed on this datasheet. The comparison table that follows highlights the configuration and documentation differences relevant to your selection.

Additional differences in specifications beyond the few shown above are not listed here — see each model's full specifications below.

Accessories Supplied

• Belt clip
• Clip-on 0.5" (12.7mm) microphone with 32" (81.3cm) cable
• Windscreen
• 9V battery
• Software
• USB cable
• Carrying case

Product Core & Specifications

Please review the Manufacturer's Data Sheet to verify published specifications. Feedback on this webpage is always welcome — please reach out to your Test Architect at any time for questions or concerns. Thank you, we truly appreciate you being our customer.