Satellite IoT and Direct-to-Device Links

What this category isn't

To set scope cleanly:

• Not Starlink, OneWeb, Kuiper. Those are LEO broadband — tens of Mbps with a pizza-box terminal. Different power budget, different cost, different threat model.
• Not amateur HF data. HF Data Modes use ionospheric skywave with no per-message fee. Satellite IoT uses commercial constellations with subscriptions.
• Not direct-to-cell. Apple iPhone 14+ Emergency SOS via satellite is a specific Globalstar implementation; Starlink/T-Mobile direct-to-cell is a different (broader-bandwidth) product.

Satellite IoT is for: a remote sensor that needs to phone home a few times a day, a hiker who wants to send "I'm OK" from the backcountry, a sailor outside cellular range, a logistics asset reporting location across an ocean.

The constellations

Iridium

Iridium operates 66 LEO satellites in cross-linked polar orbits — the only constellation with true global coverage including the poles. Originally deployed 1997-1998, near-bankrupt 2000, rebuilt as Iridium NEXT 2017-2019.

Two relevant services:

• Iridium Short Burst Data (SBD) — store-and-forward 340-byte messages either direction. Standard latency ~10-20 seconds when a satellite is overhead. Used by Garmin inReach, ZOLEO, RockBLOCK modules (rock7.com), and most marine and aviation tracking devices.
• Iridium Certus — broadband (up to ~700 kbps), different terminal class, used by maritime and government.

Pricing for SBD via consumer products like Garmin inReach: $15-65/month for various message-volume tiers. Direct via RockBLOCK: ~$0.12 per message plus a monthly line rental.

Coverage: truly global, including poles, oceans, and mid-Pacific.

Globalstar

Globalstar's constellation (24 LEO satellites) is the carrier behind:

• Apple iPhone 14+ Emergency SOS via satellite (2022 onwards). Free for two years from device activation, then a paid subscription that Apple has been extending. The phone has a custom Globalstar antenna; messages route through Globalstar to terrestrial gateways, then to dispatch services.
• SPOT trackers — older consumer devices for hiking and adventure, one-way and two-way variants.
• Various B2B IoT services.

Coverage: most of the populated world but not the poles. Real-world latency ~30-60 seconds.

The Apple deal (announced 2022, extended 2023-2024) effectively put Globalstar in 100M+ pockets and made satellite SOS a default consumer expectation.

Swarm — winding down

Swarm Technologies launched a constellation of small (sandwich-sized) satellites starting 2018. Notable for:

• Aggressive pricing: $5/month for ~750 short messages, $119 for the M138 ground modem.
• Tiny ground modules, low power, simple UART interface.
• Acquired by SpaceX in August 2021.

In April 2024 SpaceX announced Swarm would be decommissioned, with service ending in stages through 2025-2026. Existing satellites are being deorbited, gateways are being shut down. The customer story is migration to Starlink direct-to-cell or to other narrowband providers.

If you read older off-grid documentation that recommends Swarm, that recommendation is no longer current. The constellation is going away.

Astrocast

Astrocast is a Swiss operator running a small constellation (~10-20 cubesats) at low altitude. Their protocol is custom and L-band-based, similar in spirit to LoRaWAN (low duty cycle, narrowband, asynchronous). Modules cost ~$50-100; service plans start under $1/month for very low volume.

Targeting industrial M2M: agriculture, oil and gas, asset tracking. Coverage: not continuous; messages are queued and delivered when a satellite passes overhead, latency from minutes to hours.

Project: astrocast.com.

Lacuna Space

Lacuna runs a small LEO constellation that listens for standard LoRaWAN uplinks. A LoRaWAN sensor that already works on the ground also reaches Lacuna's satellites with the same modem and same firmware — just with the sat-side gateway in orbit instead of on a tower.

This is a fundamentally different go-to-market: instead of selling a proprietary radio, Lacuna sells coverage for the radios that the LPWAN ecosystem already shipped. Power-efficient, cheap modems ($5-15), but very low data rate (a few hundred bytes per pass).

Project: lacuna.space.

Other operators (briefly)

• Inmarsat — older GEO constellation (3 high-orbit sats), longer latency, used by maritime industry. BGAN service for higher data rate.
• Orbcomm — long-running M2M operator, used in fleet tracking; less consumer-visible.
• Hiber — Dutch IoT cubesat operator, paused operations 2022.
• Sateliot — Spanish 5G NB-IoT-via-satellite operator, in deployment 2024-2026.

Comparison

How payload encryption sits

This matters and is often glossed over: the satellite operator sees all metadata. Source identity, destination, time, message size, often message content unless the user encrypts.

For a Garmin inReach or ZOLEO, the consumer sees their messages routed through the manufacturer's portal, then to SMS / email. The portal sees plaintext unless you encrypt above it. The "Iridium sees plaintext" point is the same.

If confidentiality matters: encrypt the payload before passing it to the modem. A 340-byte SBD slot easily holds a Curve25519+AES-GCM ciphertext of a 100-byte message. PGP-encoded text fits when compressed. This is purely an application-layer concern; the constellation is a transport.

The metadata — that you sent a message at a certain time from approximately some location — cannot be hidden. The constellations track it as part of operating the network.

Threat model

What satellite IoT does:

• Provides global reach without local infrastructure.
• Survives terrestrial outages: cellular, internet, fiber cuts, power.
• Works (mostly) under hostile RF conditions where cellular gets jammed selectively but satellite frequencies are harder to jam locally.

What it doesn't:

• Operator can comply with subpoenas, lawful intercept requests, and most US-jurisdictional pressure (Iridium, Globalstar, SpaceX/Swarm are US companies; Astrocast is Swiss; Lacuna is Dutch — jurisdiction varies).
• Operator can disable a device's account; service is permissioned.
• The satellite uplink is an RF signal; broad-area direction-finding by capable adversaries is feasible.
• Encryption of payload is on you. Default products (Garmin inReach, etc.) do not E2E-encrypt user content from the operator's portal.

If your threat model is "I want a state-resistant communication channel," satellite IoT is one transport in a stack — with payload encryption layered on top — not a complete answer. If your threat model is "the internet went down in my country and I need to reach the outside world," it is excellent for what it is.

When to use which

• Two-way messaging in the global backcountry, including poles: Iridium SBD via Garmin inReach or ZOLEO. The reference choice for serious expedition use.
• Emergency SOS from a smartphone you already own: Apple iPhone 14+ (Globalstar) or, increasingly, Android phones with Snapdragon Satellite (Iridium-backed) and Samsung's emerging direct-to-cell. Free or cheap, low-friction.
• Battery-powered sensor reporting once or twice a day: Astrocast (custom modem) or Lacuna Space (LoRaWAN modem). Cheaper than Iridium per-message at low volume.
• You were planning to use Swarm: don't. Pick another provider (constellation winding down).
• You need broadband, not narrowband: Starlink Mini or Iridium Certus, depending on power budget and latency tolerance.

Combining with other off-grid tools

A typical layered off-grid stack:

Local mesh ── LoRa ── [Meshtastic] ── Bluetooth ── Phone with sat modem ── Iridium SBD

Or:

[Reticulum over LoRa] ── gateway node ── [Reticulum over Iridium SBD]

Reticulum's transport-agnostic design (Reticulum) makes it natural to bridge a local LoRa mesh to a satellite SBD link. Encryption is handled by Reticulum end-to-end; the satellite operator carries opaque ciphertext.

For HF as an alternative (no per-message fee, no operator dependence, but no encryption legally allowed on amateur bands), see HF Data Modes.

Ecosystem realism

• Costs are not trivial for high-volume use. A device pinging position every 10 minutes can cost $50-200/month.
• Modems use real power. Iridium SBD transmits at a few watts; sustained polling drains batteries that last forever in low-power LoRa mode.
• "Always-on" is not the operating model. Send when you have something to send.
• Two-way latency varies hugely. Iridium ~10-20 s; Astrocast / Lacuna can be hours.
• Globalstar/Apple Emergency SOS is genuinely lifesaving for the case it covers (lost in mountains, can't make a call) but is not a free messenger replacement.

Primary sources

• Iridium Short Burst Data — iridium.com/services/sbd.
• Garmin inReach product line — garmin.com/en-US/c/sports-fitness/inreach-satellite-communicators.
• ZOLEO — zoleo.com.
• RockBLOCK 9603 module — rock7.com.
• Globalstar — globalstar.com.
• Apple Emergency SOS via satellite — apple.com/newsroom/2022/11/emergency-sos-via-satellite-makes-its-debut-today-on-the-iphone-14-lineup.
• Swarm acquisition by SpaceX (August 2021) and decommissioning announcement (April 2024) — spacenews.com coverage; Swarm operator notices.
• Astrocast — astrocast.com.
• Lacuna Space — lacuna.space. LoRaWAN spec — lora-alliance.org.
• Inmarsat BGAN, Orbcomm, Sateliot — operator websites.

Continue with Satellite broadband and direct-to-cell.