Compare Cloud and On-Device AI Costs Without Inventing Energy Numbers

“On-device AI saves battery” and “cloud AI is more efficient” can both sound plausible. Neither is a measurement. The placement decision crosses at least four different budgets: user wait + network transfer + provider spend + device energy Do not collapse them into one vague “cost” number. Measure each with its own unit and evidence boundary. Start by identifying the actual execution path I reviewed MonkeyCode mobile code at commit c58bcd4 . The task stream opens a server-supported WebSocket. The speech-to-text hook also participates in a server-supported streaming path. That reviewed path is not evidence of on-device model inference. So a fair current study would measure a mobile client using remote task and voice services. An on-device alternative would be a separate prototype with its model, runtime, and packaging declared. Record a measurement envelope The included CSV template begins with these fields: sample_id,sample_kind,placement,device,os,framework,model,network,input_tokens,output_tokens,latency_ms,bytes_up,bytes_down,energy_joules,cost_usd Why so many? device , os , and framework make thermal and runtime results interpretable; model and token counts keep workload size visible; network separates offline, Wi-Fi, and cellular behavior; latency is milliseconds, transfer is bytes, energy is joules, and provider spend is currency; sample_kind prevents synthetic examples from masquerading as device measurements. Battery percentage is too coarse for short runs. It is affected by display, radio, background work, battery health, temperature, and OS estimation. If you cannot collect energy with an appropriate platform profiler or external power measurement, leave energy_joules empty. Use matched user flows Compare the same tasks, not unrelated model demos: Flow Cloud case On-device case Short prompt Same input and output cap Same semantic task and cap Voice turn Same audio fixture Same audio fixture Offline Expected failure or queued action Local completion if supp