Scope: Personal Emergency Response Systems (PERS) worn or placed at home to summon help in a medical emergency — in-home base-station units, mobile/on-the-go GPS wearables, and hybrid systems. Excludes medication dispensers/reminders devices (adjacent product, noted below) and hospital nurse-call/bed-exit systems (different buyer and install context).

Seed:
1. Equivalent of steel hardness: help-button range in feet / backup-battery hours is a spec that only means something as one side of a trade-off — a fixed in-home base station gets long range but only ~32h of backup power, while a battery-only mobile pendant runs 24h-5 days but depends on cellular coverage.
2. An industrial designer would notice first that "fall detection" is sold as a sensor add-on bolted onto the same pendant hardware, not a different device — the SKU difference is a firmware/service flag, not a BOM change, which is why it's priced as a recurring fee rather than a one-time part cost.

Sources:
[wiki_medical_alarm] en.wikipedia.org/wiki/Medical_alarm — defines PERS variations (mobility, who's notified, device location, sensors, communication, monitoring-center UL approval, dead-man's-switch "safety check") — fetched body text, TOC sections Variations/Monitoring centers/Costs
[ul_1637] shopulstandards.com/ProductDetail.aspx?productId=UL1637 — UL 1637 "Home Health Care Signaling Equipment," Ed.5, covers signal-initiating devices + central-station receiving equipment — fetched standard scope text directly
[medicalguardian_specs] medicalguardian.com/medical-alert-systems — comparison table: Help Button Range 1,400 ft, Backup Battery Life 32h (home)/up to 5 days or 24h (mobile), Water Resistant, GPS, Fall Detection as add-on, Plan Type Lease/Buy, Step Counting, UL-certified monitoring center — fetched table text
[mobilehelp_specs] mobilehelp.com/pages/medical-alert-systems — "Fall Button does not detect 100% of falls," AT&T network dependency disclaimer, pendant/wristband wearable form, U.S.-based operators — fetched page text
[bayalarm_specs] bayalarmmedical.com — 800-1,000 ft range, 72h hybrid / 36-48h mobile battery, 5-Diamond CSAA certified monitoring, <45s typical response claim, one-time $89.40 device fee, no long-term contracts, SOS Smartwatch product — fetched page text incl. embedded product JSON-LD
[caring_buyers_guide] caring.com/senior-products/best-medical-alert-systems — comparison table columns Fall Detection/GPS/Activity Tracking/Caregiver Portal/Medication Reminders/Multilingual; "whether equipment is leased or purchased outright"; equipment/activation fees can push cost over $200; two-way comms sometimes base-unit-only — fetched page text

Branches:
- system_type (in_home / mobile_on_the_go / hybrid_both): in-home base stations have a fixed help-button range and landline-or-cellular choice; mobile wearables trade that range for GPS + carrier-network dependence — medicalguardian_specs table splits Home vs On-The-Go with different fields.
- monitoring_type (professionally_monitored / self_monitored_contact_list / direct_dial_emergency_number): wiki_medical_alarm's "Who gets notified" / "Types of providers" sections name all three as real, separately-sold variants.
- connection_type (landline / cellular): medicalguardian_specs sells both as separate SKUs with different connection-dependent fields (no GPS on landline).

Noise (spec-sheet rows with no facet):
- "MyGuardian Portal" / app login UI polish — software feature, not a comparison axis a buyer judges across brands.
- "OnGuard Notifications" (text/email alerts to caregiver list) — folded into caregiver_app_or_portal; too granular for its own facet.
- Medication dispensers (pill-release hardware) — caring_buyers_guide lists as adjacent category, different device entirely.
- "Smarti Voice Assist" self-test branding — vendor-specific marketing name for a self-diagnostic feature, not a cross-brand axis.
- Specific $ promo codes / sale pricing — temporary marketing, not a stable facet.

Corrections (2026-10-26):
- Added `one_time_fee_usd` facet (evidence: bayalarm_specs' $89.40-$159.20 tiered device fees, caring_buyers_guide's >$200 combined-fee note) and rewrote `first_year_cost`'s formula/depends_on to use it, replacing the undefined `one_time_device_or_activation_fee` variable.
- Added `monitoring_language_support` facet (english_only / multilingual_support_available), evidenced by bayalarm.com's own "Multi-Language Support" section (180 languages) plus caring_buyers_guide's repeated multilingual callouts.
- Dropped `connection_type` from `system_type`'s `hybrid_both` branch `then_ask` — Bay Alarm's real hybrid/all-in-one product (SOS All-in-One) has no landline/cellular base-station choice, only `gps_location_tracking` remains asked on that leg.
- Re-annotated `monthly_monitoring_fee`'s range: `typical` now names which brand/plan hits each bound ($24.95 Medical Guardian/MobileHelp annual, $47.95 Bay Alarm VIPx, both via caring_buyers_guide) and states explicitly that bayalarm_specs' own $27.95-$39.95 standard pricing sits inside the range without hitting either bound, rather than implying it corroborates the bounds. Did not change the numbers themselves — no independent second source for a different floor/ceiling was found.
- Added `location_assist_technology` facet (gps_only / gps_and_wifi_assisted) to capture Bay Alarm's "GPS/Wi-Fi positioning" marketing, which targets the register's own flagged indoor-GPS-accuracy weakness. Single-sourced to bayalarm_specs (confirmed in two places on the page); no second source found after checking medicalguardian/mobilehelp/caring pages, so marked `backfill_cost: high` and noted as a single-brand observation.
- Relabeled `pricing_model`, `monthly_monitoring_fee`, and `upfront_fees_and_contract` from `source: "listing"` to `source: "researched"` — their own `listing_field_hint`s describe a brand pricing/checkout page, not a field most retail listings carry.
- Rejected the check.md note on the ambiguous "System Status" row (medicalguardian_specs table) — it was flagged as not a required fix ("worth a second look," not filed), so left as-is this run.