OTA firmwares cannot be restored to. IPSW Downloads collects them for potential future use. They might also be useful if you're doing research.
| ✗ | Apple Watch Series 4 (44mm, LTE) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.4 GiB | d878d0587788f47a9a7abbfbdb6c9459c17dca44.zip |
| ✗ | Apple Watch Series 4 (44mm, LTE) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.4 GiB | f3f4b592793574971d0b4eea51b6d7f49a0074c1.zip |
| ✗ | Apple Watch Series 4 (44mm, LTE) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.4 GiB | d03b0c5bb52ae0794522bc2bce34c2c872053336.zip |
| ✗ | Apple Watch Series 4 (44mm, LTE) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.4 GiB | 8b7ee66d1c13602a555dace37f8137999fd08aa5.zip |
| ✗ | Apple Watch Series 4 (40mm, LTE) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.4 GiB | 3c5238738fd5d3c7584e7fc00223f36330cc140e.zip |
| ✗ | Apple Watch Series 4 (40mm, LTE) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.4 GiB | bd648b48b8fcbd239a20c8ec2b3d1f27fe46162e.zip |
| ✗ | Apple Watch Series 4 (40mm, LTE) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.4 GiB | 5eaf585c4a80c85df92912594ee4d4c28a128e60.zip |
| ✗ | Apple Watch Series 4 (40mm, LTE) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.4 GiB | f989902aa070260bcf530d0e77efff1a4debb127.zip |
| ✗ | Apple Watch Series 4 (44mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | 8e1f17e917ac762b6daa4d631f494c20ac27b9d4.zip |
| ✗ | Apple Watch Series 4 (44mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | 40bd82b3eb066c1064ace547e5e218bafd0f789c.zip |
| ✗ | Apple Watch Series 4 (44mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | ddca40d08c5ad004ce49a9494241626c85dbb605.zip |
| ✗ | Apple Watch Series 4 (44mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 4394a0b744b81d99db5feb6b12a19cfe3c4d2e4f.zip |
| ✗ | Apple Watch Series 4 (40mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | 6ca24d7715d907e0a136fe1db9fc1055d1ea7ea0.zip |
| ✗ | Apple Watch Series 4 (40mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | c0f641772ff95c77f3f6c143ea30ed27abcd7d14.zip |
| ✗ | Apple Watch Series 4 (40mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | 53c0ea7bd7f8d44d6ad442a05e9b44dac9e1eb74.zip |
| ✗ | Apple Watch Series 4 (40mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 5efa1b9d556d98b509434625501094453740b165.zip |
| ✗ | Apple Watch Series 3 (42mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 82deb360bbdbc57899002799e6795665d6a77e07.zip |
| ✗ | Apple Watch Series 3 (42mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | fc51c12c5dc75b9f7b46a9e94a7a094497fb06d1.zip |
| ✗ | Apple Watch Series 3 (42mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | b6b6782ce393d5dd0ce4ece0b1847e040a61ce41.zip |
| ✗ | Apple Watch Series 3 (42mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | 10f8796e3b78ca3bcad22426d6aa415163016b9f.zip |
| ✗ | Apple Watch Series 3 (38mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 63062ede68a91d62282c3d633b9c96f9a3a4cbbe.zip |
| ✗ | Apple Watch Series 3 (38mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | e6b9276d5f7224f69f35bdec3cc5d8bb0461f8ed.zip |
| ✗ | Apple Watch Series 3 (38mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | c6dacc15a6c48521b17fd18b2356947288222558.zip |
| ✗ | Apple Watch Series 3 (38mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | 62ff73b2ff61eab31576134c56d50197249528e7.zip |
| ✗ | Apple Watch Series 3 (42mm, LTE) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | d24d014147d97a1fff09fc6358de9966ad942d7f.zip |
| ✗ | Apple Watch Series 3 (42mm, LTE) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | f2c79a9e31fb22c1bbac3170ce82e75a42dccc61.zip |
| ✗ | Apple Watch Series 3 (42mm, LTE) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | c6d031d04ecac62f37592255ecbcad9632c3c992.zip |
| ✗ | Apple Watch Series 3 (42mm, LTE) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 57af8e452aa1b9f6b03ae5df47a1ffdc415008dc.zip |
| ✗ | Apple Watch Series 3 (38mm, LTE) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 2b3eb924620a86654b5a75230aacd34a98a3729a.zip |
| ✗ | Apple Watch Series 3 (38mm, LTE) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | 29cfdecdb46ac125f11e391742f85e7a35afaaf4.zip |
| ✗ | Apple Watch Series 3 (38mm, LTE) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | 6a1246ac8ed542627db268f275b20c2d3aabe248.zip |
| ✗ | Apple Watch Series 3 (38mm, LTE) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | adc9678be5d080720232e01362ebc64338f3c1e4.zip |
| ✗ | Apple Watch Series 1 (42mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | 58c15e771f09819889e27a3502e9e809ab9b3c96.zip |
| ✗ | Apple Watch Series 1 (42mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 15339af604e23c1c4cc8772c99d845d975d2cf31.zip |
| ✗ | Apple Watch Series 1 (42mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | c0215020e84367caf890374538a3aae9826a5e87.zip |
| ✗ | Apple Watch Series 1 (42mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | 926638bd83a9b96b8209a2cd7f8dea8c4902f7af.zip |
| ✗ | Apple Watch Series 1 (38mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | 778782ff0c298fdb8f06f9d1fecdd7f2319ca200.zip |
| ✗ | Apple Watch Series 1 (38mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | 78daadb529061c4d8247dae374d821060102fb78.zip |
| ✗ | Apple Watch Series 1 (38mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | 054c0805575e57adda99e5ee58665383b279fafb.zip |
| ✗ | Apple Watch Series 1 (38mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | b4de988c2cdb429012f26a7760d01f653f380ef5.zip |
| ✗ | Apple Watch Series 2 (42mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | dbfa217345a487d2669b4c0bd140dda1c3bf00ec.zip |
| ✗ | Apple Watch Series 2 (42mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | b43fd81b22cc45d42bf83180f25cb77531124618.zip |
| ✗ | Apple Watch Series 2 (42mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | 63fa68b2932c5ede607cd590ed1653547d78d1ab.zip |
| ✗ | Apple Watch Series 2 (42mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | f33d74fd594a85ec88aed95edc6fc06fc647d9e9.zip |
| ✗ | Apple Watch Series 2 (38mm) | watchOS 5.1.3 (16S535) | January 22, 2019 | 1.3 GiB | 425d87c338ba128c47bd359a1dfd09a5c1006700.zip |
| ✗ | Apple Watch Series 2 (38mm) | watchOS 5.1.3 (16S5523a) | December 10, 2018 | 1.3 GiB | b5eea432d4d65ed483bd05dbba1c142df2354dcb.zip |
| ✗ | Apple Watch Series 2 (38mm) | watchOS 5.1.3 (16S5531a) | December 19, 2018 | 1.3 GiB | 04118e32923602c0865112c26229521080f4a148.zip |
| ✗ | Apple Watch Series 2 (38mm) | watchOS 5.1.3 (16S5535a) | January 7, 2019 | 1.3 GiB | 5210277fd6f1bfcf63037b1000a338870f4eb09f.zip |