Como dizer "Baixar a guarda" em inglês

Guarda baixa: off guard
Ser pego com a guarda baixa: to be caught off guard

- Quintal was caught off guard when his video-taped interrogation appeared on CNN (thenewstribune.com)
- The size of the crowds caught many government and security officials off guard. (online.wsj.com)
- Reminders can be set up so users aren't caught off guard by poor time-management. (cnn.com)

As an aside comment:
As people lowered the guard for H1N1 flu, it's returning.
Baixaram a guarda no sentido de "relaxaram" as medidas sanitárias que praticavam.

Quintal was caught off guard when his video-taped interrogation appeared on CNN.
Neste caso ele foi pego 'de surpresa/sem esperar' ou de "calça curta"- se podia ter previsto ou não é outra questão (ou seja, é irrelevante pra situação, o foco é que 'foi pego desprevenido" (fator surpresa).

To drop the guard

You’ve got to remain professional, but as long as bulletproof respect has been established early on, dropping the guard every now and then is a good thing. Ref. theguardian