Signing a rental reservation by SMS: a certified contract with OTP
· 3 min read
The perfect tenant views the flat on Saturday and by Monday has already rented another one. In a market that moves in hours, asking people to print, sign and scan a reservation means losing deals. The alternative: send the document to the phone and have it signed with a one-time code, with an evidence file.
How it works
- You upload the reservation document (PDF) and the signer's number.
- They receive an SMS with a link to our portal, where they read the whole document before signing.
- They press sign and receive an OTP code by SMS that they must enter. The code is bound to their number: whoever signs proves they hold that phone.
- The file records every step — delivery, opening, reading, verified code and signature — chained with cryptographic fingerprints and with a qualified Camerfirma timestamp on the daily anchor.
The legal value, without embellishment
- Under Spanish law, contracts are formed by consent and are valid whatever their form (arts. 1254 and 1278 of the Civil Code). A rental reservation or an earnest-money agreement does not require paper.
- The resulting signature is a simple electronic signature, and the eIDAS Regulation (art. 25.1) prevents it from being denied legal effect for being electronic. It is not a qualified signature and we do not say so anywhere: what you are buying here is the proof of who signed, which exact document and when.
- If someone challenges it, it is proven with the file and, where appropriate, an expert report (art. 326.3 of the Civil Procedure Act): the document's fingerprint, the OTP bound to the number, the access traces.
Details that matter in real estate
- The document does not travel by SMS: a link to a secure portal with an expiry date does. Nobody forwards a PDF with personal data over an open channel.
- The PDF's fingerprint stays in the file: if “another version” of the document turns up tomorrow, it is detected.
- It works just as well for renewals, annexes, signed inventories and viewing authorisations.
The questions agencies ask us
What if the signer does not have a smartphone? Any mobile phone can receive the code: the document is read in a browser — theirs or that of any device where they open the link —, and the OTP arrives by ordinary SMS.
How long does the link last? It expires — after 30 days by default — and that expiry is recorded in the file. A document cannot stay signable forever in a forwarded chat.
Who keeps what? The file and the PDF certificate stay in your account, downloadable; the recipient keeps their access while the link is valid. The certificate PDF includes a code with which any third party can verify it on our public page — a court included.
A contract with two signers? Each file certifies one signature on one document. For landlord and tenant, two files are sent with the same PDF: two signatures, two pieces of evidence, the same document fingerprint.
The price is that of the carrier SMS plus the certified supplement — published rates —, and you can try it in test mode without spending anything.