Security deposit (Mietkaution).
Tenant's security deposit, in Switzerland held on a blocked bank account.
A security deposit (Mietkaution, also called Mietzinsdepot in German-speaking Switzerland) is money the tenant puts up as security for the landlord. In Switzerland it can be at most three months' rent and must sit in a blocked account at a Swiss bank in your name. The landlord has no direct access to it. At the end of the tenancy, if there are no open claims, the deposit plus interest is released back to you.
Alternative: deposit insurance (e.g. SwissCaution, FirstCaution) instead of cash in a blocked account. You pay an annual premium (~4-5% of the deposit amount) and the insurer provides the guarantee. Upside: no capital tied up. Downside: the premiums are not refundable.
If you already have a deposit or deposit insurance in place, you can note it in your Tenant Passport on aptari. It strengthens your profile when you apply.