It's the SAS Control module.
It contains the shock sensor which decides if an impact is serious enough to deploy airbags and seat belt tensioners.
It also monitors the system to ensure bags don't deploy if a fault occurs.
SAS CONTROL MODULE REMOVAL/INSTALLATION
2007 Mazda MX-5 Miata Sport
2007 RESTRAINTS Air Bag System - MX-5 Miata
1. Perform SAS control module configuration when replacing it. (See SAS CONTROL MODULE
2. Turn the ignition switch to the LOCK position.
3. Remove the battery cover.
4. Disconnect the negative battery cable and wait for 1 min or more . (See BATTERY
REMOVAL/INSTALLATION [LF] .)
5. Remove the following parts:
1. Console (See CONSOLE REMOVAL/INSTALLATION .)
2. Side wall (See SIDE WALL REMOVAL/INSTALLATION .)
3. Console panel (See CONSOLE PANEL REMOVAL/INSTALLATION .)
6. Remove in the order indicated in Fig. 18 .
WARNING: Handling the SAS control module improperly can accidentally
deploy the air bag modules and pre-tensioner seat belt, which may
seriously injure you. Read the air bag system service warnings and
cautions before handling the SAS control module. (See AIR BAG
SYSTEM SERVICE WARNINGS .) (See AIR BAG SYSTEM SERVICE
CAUTION: Handling the SAS control module improperly can accidentally deploy
the air bag modules and pre-tensioner seat belt, which may seriously
injure you. If configuration is not completed before removing the SAS
control module, DTC B2477 will be displayed.
Black 2005 NCLE GWR Exh, Cosworth, Mototune, Ohlins, PF01