Why a "LoRa chip" can hear 433 MHz remotes
LoRa is a modulation (chirp spread spectrum). Some Semtech "LoRa" transceivers also contain an ordinary FSK/OOK modem. The SX1276/77/78/79 datasheet lists LoRa, FSK, GFSK, MSK, GMSK and OOK. Cheap 433 MHz remotes, door/PIR sensors and many weather sensors send OOK (on/off keying, a form of ASK). The EV1527 devices in the reed switch thread and the remote thread are OOK pulse trains. A few sensors use FSK instead. If the chip has an OOK modem, you tune it to 433.92 MHz, put it in OOK mode and let software decode the pulse timings.
LoRa modulation itself cannot decode these devices. You have to take the chip out of LoRa mode and into OOK (or FSK) mode. Then you are using it as a generic receiver, and the LoRa part is idle.
Which chips can and can't
- SX1276/77/78/79 (SX127x), including RFM9x-style modules and the Ai-Thinker Ra-01 (SX1278): yes. OOK and FSK, in packet mode or continuous mode. The datasheet gives an OOK bit rate of 1.2 to 32.768 kbps and about -117 dBm OOK sensitivity at 4.8 kb/s under its lab test conditions. Real-world range will be worse.
- SX1261/62/68 (SX126x) and LLCC68: no OOK. Semtech lists LoRa and (G)FSK for these (the SX1262 also has LR-FHSS, transmit only). I found no OOK mention in the SX1262 datasheet, and ESPHome's sx126x component only offers LoRa and FSK. DIO2 on these chips is normally an RF switch control, not a raw data output, so the continuous-mode trick below does not apply. Some FSK sensors might be reachable in packet mode if their framing happened to match, but I have not seen a documented rtl_433-style receiver built on SX126x.
- LR2021 (newer): Semtech's page lists OOK among its modulations and RadioLib's README lists it as LoRa/GFSK/LR-FHSS/FLRC/OOK. The datasheet wording on OOK receive is unclear to me, there are few boards, and none of the 433 MHz projects below target it. Treat it as unproven for this job.
How the SX127x hands you the data
- Packet mode: the chip's packet engine wants a preamble, a sync word and usually a length and CRC. Most OOK remotes and sensors do not frame their data that way, so this suits links you design yourself, not generic devices.
- Continuous mode: the demodulated bit stream comes out raw on the DIO2 pin. A microcontroller such as an ESP32 timestamps the edges, and software decodes the pulse widths and gaps. That is how rtl_433_ESP and ESPHome's sx127x plus remote_receiver combination work. The datasheet describes an optional bit synchroniser that outputs a clock on DIO1. ESPHome recommends enabling it in continuous mode, but says to try turning it off if there is no preamble and high noise.
- OOK threshold: the chip's OOK demodulator compares the signal strength against a threshold, so noise tuning matters. rtl_433_ESP exposes OOK_FIXED_THRESHOLD, and ESPHome has an rx_floor setting. Set it too sensitive and you decode noise, too deaf and you miss weak sensors.
- OOK/ASK: the carrier is switched on and off. Simple and cheap, which is why most basic 433 MHz gear uses it.
- FSK: the frequency shifts between two values. Some sensors use it, but chip packet settings rarely match them. OpenMQTTGateway ships separate -fsk builds, and the rtl_433_ESP README says FSK and OOK demodulation cannot run at the same time.
- LoRa: chirp spread spectrum. Great range at low data rates, but it is its own protocol. It cannot be pointed at a random remote.
- Chip versus board: the SX1278 covers 137 to 525 MHz. The SX1276/77 cover 137 to 1020 MHz and the SX1279 137 to 960 MHz. An SX1276 on a 868/915 board can be tuned to 433 in software, but the matching network, filter and antenna on that board are built for the other band. I would expect poor sensitivity, so buy the 433 MHz variant. The rtl_433_ESP docs give the same warning about frequency variants.
- Antenna: a quarter-wave wire is roughly 17 cm at 433.92 MHz. The rtl_433_ESP author says a vertical antenna helps, and that these receivers get about half the range of an RTL-SDR or less.
- 433.92 MHz: most devices sit there, but some are elsewhere in the band, so check what your device actually uses.
In the LIPD Class Licence 2025 (F2025L01047) I found an entry for 433.05 to 434.79 MHz: any transmitter, maximum 25 mW EIRP, no additional limitations. That covers transmitting. I did not find anything about receiving from your own devices, but check the ACMA page for details and later amendments: LIPD class licence. Equipment also has to meet the relevant standards, which I have not looked into.
Related reading
- Overview of Zigbee, Z-Wave, LoRa and 433 in Australia: thread 116
- No LoRa chip needed, an RTL-SDR with rtl_433: thread 117
- LoRa chips compared: thread 133, and open source projects: thread 134
- Sources: SX1276/77/78/79 datasheet, SX1262, LLCC68, rtl_433_ESP, ESPHome sx127x