Halacha Is a Specification, If You Write It Like One

The most common failure in developing a Shabbat-compliant product is not engineering. It is documentation. A rabbinic authority gives an opinion in conversation, an engineer interprets it, firmware gets written, and eighteen months later the certifying agency rejects a behavior nobody wrote down. The rework is expensive and entirely avoidable.

Halachic requirements behave like safety or regulatory requirements. They are constraints on system behavior, they can be stated in testable language, and they belong in the same controlled document as everything else. The discipline in how to write a product requirements document applies unchanged. What differs is who reviews the document and how the acceptance tests are written.

Turn an Opinion Into a Requirement

A ruling arrives as a sentence like "the user should not directly cause the heating element to turn on." That is a principle, not a requirement: nobody can build against it or verify it.

The conversion has four parts. State the observable behavior, not the intent. Bind it to a specific subsystem. Give it a numeric bound wherever a threshold exists. Attach a pass/fail test.

The example above becomes: REQ-SH-014. When the front panel Heat control is actuated during Shabbat mode, the controller shall not change the heater output state as a direct result of the actuation. The controller shall register the request and shall apply the requested state only at the next scheduled evaluation point, which shall occur at a fixed interval of not less than 15 seconds and not more than 60 seconds, independent of the actuation time. Verification: instrument the heater drive line, actuate the control 50 times at random offsets within the interval, and confirm zero state transitions within 15 seconds of any actuation.

That version is buildable, testable, and reviewable. It also exposes the questions worth asking the posek before code exists: must the interval be fixed or randomized, is a pending request discarded if the mode ends, and does an indicator light count as a state change.

The Clauses That Recur in Almost Every Product

Different products, similar spec sections. Drafting from this list saves a review cycle.

  • Direct causation. No user action may directly complete or break an electrical circuit during the restricted period. This is usually satisfied by an indirect-action architecture, and the mechanisms available are surveyed in grama mechanisms. Specify the decoupling method, the interval, and whether the interval is fixed or randomized.
  • Sensor response. Motion, proximity, capacitive, load, and door sensors all create a causation problem. State for each sensor whether it is disabled, ignored, or polled on a timer during the restricted period, and what the system does with the data.
  • Indicators and displays. Define exactly which LEDs, segments, and screen elements may change and when. A display that updates on user action is a state change even when nothing else moves. Many designs specify that indicators freeze or run on the same timed evaluation as outputs, a point covered in what Sabbath mode on appliances is and how it is engineered.
  • Audible feedback. Beeps, chimes, and voice prompts need an explicit rule, typically suppressed entirely.
  • Automatic and adaptive behavior. Thermostat cycling, defrost, compressor control, auto-shutoff timers, and firmware optimization all keep running. State for each whether it continues unchanged, must be pre-set, or must be suspended.
  • Scheduling and calendar. If the product enters and exits the mode automatically, specify the time source, location source, boundary calculation method, tolerance in minutes, and behavior on power loss. Products relying on external scheduling instead are discussed in Shabbat timers and controllers.
  • Mode entry and exit. How the user enters, whether entry is reversible, what happens on an attempted exit mid-period, and what state the product resumes in.
  • Failure behavior. What the product does on sensor fault, network loss, brownout, or watchdog reset during the restricted period. A product that reboots into normal mode has failed regardless of how good the main logic is.
  • Materials and contact. For anything touching food, cover food-contact compliance, cleanability, and whether a component is intended to be kashered, including the temperature it must survive.
  • Content and connectivity. For media and connected devices, filtering rules, telemetry behavior, and whether the device may transmit at all during the restricted period.

Write Verification Alongside Every Requirement

A halachic requirement without a verification method will be argued about at certification. Pair each with a method and a target.

Most verify by instrumented test: a logic analyzer or current probe on the output drive, a scripted actuation sequence, and a pass criterion expressed in timing. Some verify by inspection of schematic or firmware source, particularly negative requirements about what a subsystem must not do. A few verify by demonstration in front of the reviewing authority, and those set schedule, so identify them early.

Build a traceability matrix: requirement identifier, the ruling or reviewer that generated it, the subsystem implementing it, the test case verifying it, and current status. Certifying agencies respond well to this because it is the evidence structure they need, and it turns a review from a conversation into a walkthrough. What that review involves is described in halachic certification for products.

Who Sits at the Table

Four roles, and skipping any one of them creates rework.

The rabbinic authority issues rulings. Engage one specific posek or agency early and stay with them, because different authorities reach different conclusions and a product designed to satisfy all of them satisfies none of them well.

The certifying agency reviews and marks the product. Star-K and comparable bodies publish requirements for common appliance categories, and reading their criteria before writing your spec is free.

The systems engineer owns the requirements document and traceability matrix, and pushes back when a ruling is stated in unverifiable language.

The product owner decides scope. Not every accommodation is worth its cost, and some create usability problems for most buyers. A 45-second response delay is fine on a hot water urn and unacceptable on a light switch, which is why the smart-home category converged on the patterns in kosher smart home automation.

Freeze It Before Firmware

Halachic requirements are architecture-defining, not features. A decoupled evaluation loop, a hardware interlock, or a separate mode-control processor cannot be retrofitted into firmware written around direct user control. Get the ruling, write the requirements, get them reviewed in writing, then design. Companies adding a compliant mode to an existing product face the harder version of this, described in adapting a successful product for the Orthodox market.

Get the Requirements Written Properly

Projects House writes and maintains halachic requirement sets as part of a normal engineering specification: testable statements, verification methods, traceability to the reviewing authority, and an architecture that can actually satisfy them. Send your product concept and the authority you are working with through our contact form.